English Words: U
23,789 words · Page 25 of 476
A nearly perfect vacuum; i.e. an almost or fully complete absence of matter, especially a gas at very low pressure.
Unnecessary, unprovoked (usually brutal) violence; violent acts simply for the thrill and entertainment of it.
Of electromagnetic radiation beyond (higher in frequency than) light visible to the human eye; radiation with wavelengths from 380 to 10 nanometres.
A fault in classical physics, from the Rayleigh's law/Rayleigh-Jeans law outcomes at short wavelengths/high frequencies, that causes infinite amplification of shorter wavelength/higher frequency radiation inside a cavity, due to the application of equipartition theorem on black body radiation within a cavity.
At the ultraviolet end of the spectrum, higher in frequency than light visible to humans.
Spelling & Dictionary Insight
The English alphabetical index for the letter U contains 23,789 headwords drawn from our Wiktionary-derived dictionary table. At 50 entries per page the browse splits into 476 pages, and you are currently viewing page 25. Every row above is a dictionary-backed entry with a canonical slug, and each links through to a full definition page with pronunciation, senses, etymology, and related-word data where available.
On this page 50 of 50 entries carry a part-of-speech tag and 50 carry at least one stored definition. Coverage varies across letters because Wiktionary volunteers build entries at different speeds for different parts of the alphabet, letters with common starting sounds (S, C, T, P) usually have the densest coverage, while less frequent starters (X, Q, Z) tend to have shorter but more specialised lists. PlainSpell surfaces whatever data is present and links back to the source when a definition is not yet recorded.
For readers using this index as a spelling reference, the guarantee is that every form you see on the list is a documented English headword, not a guess, not a derived inflection lacking a lemma row. If a word you expected to find is absent from the "U" list, it usually means the form exists only as an inflection of another lemma (e.g. a past participle stored under the infinitive) or the entry has not yet been imported from Wiktionary. Use the search bar or the misspelling lookup to resolve these cases.