What does diffraction mean?
Diffraction is the phenomenon by which waves — including light, sound, and water waves — bend and spread out when they pass around an obstacle or through a narrow opening. Rather than travelling in perfectly straight lines, waves flare into regions that would otherwise lie in shadow, and overlapping diffracted waves interfere to produce characteristic patterns of alternating intensity. The effect is most noticeable when the size of the obstacle or opening is comparable to the wavelength of the wave: a compact disc's shimmering colours arise from light diffracting off its fine grooves, and voices carry around corners because sound diffracts readily. Diffraction is central to physics and engineering, underpinning instruments such as diffraction gratings, spectrometers, and X-ray crystallography, the technique that revealed the double-helix structure of DNA. A strictly technical noun, it belongs to formal scientific writing rather than everyday speech.
nounThe bending and spreading of waves — such as light, sound, or water waves — as they pass around an obstacle or through an aperture, producing patterns of interference.
- The bending and spreading of waves as they encounter an obstacle or aperture, especially light, sound, or water waves.
- In crystallography and materials science: the scattering of X-rays, electrons, or neutrons by a crystal lattice, used to determine atomic structure.
"The diffraction of light through a narrow slit produced a striking pattern of alternating bright and dark bands on the screen."
"Sound waves undergo diffraction as they bend around the corner of a building, which is why you can hear someone speaking without seeing them."
"By analysing the X-ray diffraction data, the researchers were able to map the protein's atomic structure with remarkable precision."
Rarely used; the word is normally uncountable. The plural appears only when referring to separate instances or measured patterns of diffraction.
"The experiment recorded several distinct diffractions corresponding to different lattice planes."
X-ray diffraction is how scientists first photographed the structure of DNA — Rosalind Franklin's famous 'Photo 51' was really just a diffraction pattern.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diffraction
Diffraction derives from New Latin 'diffractionem', formed from Latin 'diffringere' or 'diffract-' meaning 'to break apart', combining the prefix 'dis-' (apart) with 'frangere' (to break). The term was introduced in connection with early seventeenth-century studies of light, most notably by the Italian physicist Francesco Maria Grimaldi, whose posthumously published work coined 'diffractio' for the bending of light around obstacles. It shares its root 'frangere' with words such as fracture, fraction, fragment, and refraction, all conveying the idea of breaking or splitting.
Related word forms
How diffraction is actually used
A technical term belonging chiefly to physics, optics, acoustics, and crystallography; it is formal in register and rare in everyday conversation. It is almost always used as an uncountable mass noun, though it can take a plural ('diffractions') when referring to distinct observed events or patterns. It carries no emotional connotation — it is neutral scientific vocabulary.
Easily confused with diffraction
Refraction is the bending of waves as they pass from one medium into another (e.g., a straw appearing bent in water), while diffraction is the bending and spreading of waves around obstacles or through openings.