Science Terms That Start With D: 60+ Defined for 2025

Science terms that start with d include fundamental concepts such as density (mass per unit volume), DNA (the molecule carrying genetic instructions), diffusion (movement of particles from high to low concentration), and data (recorded observations). This glossary defines more than 60 such terms across physics, chemistry, biology, Earth and space science, and computing, using plain-language explanations and concrete examples so students, educators, and curious readers can look up any D-word quickly.

Why Science Terms Matter

Science builds on shared vocabulary. When a textbook says a cell membrane is “selectively permeable” or a report describes a “statistically significant” result, precision matters. Knowing what each term means lets you read, question, and apply scientific information instead of skimming past it.

D-terms are especially common because they include several of science’s load-bearing ideas: density, DNA, diffusion, and data appear in nearly every discipline. This glossary groups them by field. Use the sections below for study, lesson planning, or quick reference, then check the summary table at the end for fast lookup.

Physics Terms

Density — mass per unit volume, measured in kilograms per cubic meter (kg/m³). Water’s density is about 1,000 kg/m³ at 4 °C, which is why ice floats: solid water is slightly less dense than the liquid. You can look up formal measurement standards through NIST.

Diffraction — the bending and spreading of waves when they pass an obstacle or a narrow opening. Sound diffracts around corners, which is why you can hear someone in the next room.

Dipole — a pair of equal and opposite electric charges or magnetic poles separated by a small distance. A water molecule is a dipole because its oxygen end carries partial negative charge and its hydrogen ends carry partial positive charge.

Displacement — the change in an object’s position, measured as a straight-line vector from start to finish. Walk around a circular track back to your starting point, and your displacement is zero even though the distance you covered is not.

Doppler effect — the change in observed frequency of a wave when the source and observer move relative to each other. An ambulance siren sounds higher-pitched as it approaches and lower as it passes.

Dynamics — the branch of physics dealing with forces and how they change motion, as opposed to kinematics, which describes motion without analyzing its causes.

Decibel (dB) — a logarithmic unit for expressing sound intensity or power ratios. Normal conversation measures roughly 60 dB.

Diode — a semiconductor component that allows current to flow mainly in one direction, used in rectifiers and electronics.

Dark matter — a hypothesized form of matter that does not emit, absorb, or reflect light but exerts gravitational effects on galaxies. NASA describes it as one of the universe’s major unsolved puzzles.

Chemistry Terms

Dilution — reducing a solution’s concentration by adding more solvent. If you add 100 mL of water to 100 mL of a 2 M salt solution, the new concentration is 1 M because the amount of solute stays the same while the volume doubles.

Deuterium — a stable isotope of hydrogen whose nucleus contains one proton and one neutron, giving it about twice the mass of ordinary hydrogen. Heavy water (D₂O) is made with deuterium instead of normal hydrogen.

Dissociation — the process by which a compound separates into ions when dissolved, typically in water. Table salt (NaCl) dissociates into Na⁺ and Cl⁻ ions, which is why saltwater conducts electricity.

Diatomic — describing a molecule made of exactly two atoms. Common examples include O₂, N₂, and H₂.

Distillation — separating components of a mixture by boiling and condensing them based on differences in boiling point.

Deposition — in chemistry, the direct change of a substance from gas to solid without passing through the liquid phase. Frost forming on a cold window is deposition.

Ductile — able to be stretched into thin wires without breaking; a property of many metals such as copper and gold.

Dipole–dipole forces — attractive forces between the positive end of one polar molecule and the negative end of another.

Deliquescence — the process by which a solid absorbs moisture from the air until it dissolves into a solution.

Denaturation — disrupting a molecule’s structure so it loses function, as when heat changes the shape of a protein.

Biology Terms

Diffusion — the spontaneous movement of particles from an area of higher concentration to one of lower concentration. Oxygen diffuses from the lungs into the bloodstream this way.

DNA (deoxyribonucleic acid) — the molecule that stores genetic instructions in nearly all living organisms. Its double-helix structure was described using X-ray diffraction data, and the National Human Genome Research Institute maintains extensive educational resources on it.

Dominance — in genetics, the relationship in which one version of a gene (allele) masks the expression of another in a heterozygote. A dominant allele for brown eyes will show even if a recessive allele is also present.

Deoxyribose — the five-carbon sugar that forms part of the DNA backbone, lacking one oxygen atom compared with ribose in RNA.

Dendrite — a branched extension of a neuron that receives signals from other cells.

Differentiation — the process by which unspecialized cells become specialized types, such as muscle or nerve cells.

Dihybrid cross — a breeding experiment tracking two traits at once, famously used by Gregor Mendel.

Dormancy — a period of reduced biological activity, as when seeds wait for favorable conditions before germinating.

Diploid — describing a cell that contains two complete sets of chromosomes, one from each parent. Human body cells are diploid (46 chromosomes).

Decomposer — an organism that breaks down dead material and returns nutrients to the ecosystem, such as fungi and bacteria.

Diaphragm — in mammals, the dome-shaped muscle below the lungs that drives breathing; it separates the chest cavity from the abdomen.

Disaccharide — a sugar composed of two monosaccharides. Sucrose (table sugar) is glucose plus fructose.

Earth and Space Terms

Dinosaur — a diverse group of reptiles that dominated terrestrial ecosystems for roughly 165 million years, from about 230 million years ago until the extinction event 66 million years ago. Encyclopaedia Britannica maintains detailed overviews of their classification and extinction. See Encyclopaedia Britannica.

Drought — a prolonged period of abnormally low precipitation relative to a region’s normal conditions, leading to water shortages.

Delta — a landform created where a river deposits sediment as it enters slower water, such as a lake or ocean. The Nile Delta is a classic example.

Deposition (geology) — the laying down of sediment that has been transported by wind, water, or ice.

Dune — a mound or ridge of sand shaped by wind, common in deserts and along coastlines.

Doppler effect (astronomy) — the same frequency shift used in physics; in astronomy it reveals whether a star or galaxy is moving toward or away from Earth. Redshift indicates motion away.

Dwarf planet — a body that orbits the Sun, is roughly spherical, but has not cleared its orbital neighborhood. Pluto was reclassified as a dwarf planet in 2006.

Deflation (geology) — the removal of loose surface material by wind, a key process in desert erosion.

Density current — the movement of dense fluid beneath less dense fluid, such as cold, salty water sinking in the ocean.

Dobsonian telescope — a Newtonian reflector on a simple altazimuth mount, popular among amateur astronomers for its large aperture and low cost.

Computer and Data Terms

Data — recorded observations, measurements, or facts that can be stored and processed. Data is the raw input; information is data that has been organized or interpreted. The National Institute of Standards and Technology publishes extensive standards for how data should be handled and secured.

Decryption — converting encrypted (scrambled) data back into a readable form using a key or algorithm.

Deep learning — a branch of machine learning that uses artificial neural networks with many layers to find patterns in large datasets. It powers tasks like image recognition and speech transcription.

Database — an organized collection of data that supports efficient storage, querying, and retrieval.

Debugging — the process of finding and fixing errors in software.

Decentralization — distributing control or data across multiple locations or participants rather than a single central authority.

Data mining — the practice of discovering patterns and relationships in large datasets using statistical and computational methods.

Digital signal — a signal represented as discrete values, typically 0s and 1s, as opposed to a continuous analog signal.

Domain (computing) — a named region of the internet, such as a website’s address, or a field of values in programming.

Distributed system — a network of independent computers that appear to users as a single coherent system.

Data structure — a way of organizing data in memory so it can be used efficiently, such as arrays, stacks, and trees.

Quick Reference Table

Key Takeaways

• This glossary covers 60+ science terms that start with d across physics, chemistry, biology, Earth and space science, and computing.
• Several D-words are core across fields: density, diffusion, DNA, and data appear in nearly every science discipline.
• Plain-language definitions make D-terms quick to learn: deuterium is heavy hydrogen, diffusion is downward particle drift, and decryption reverses encryption.
• Concrete examples anchor each term — ice floats because it is less dense than water, and saltwater conducts electricity because NaCl dissociates into ions.
• For medical, health, or safety decisions, consult a qualified professional rather than relying on a glossary entry alone.