"one" + adverbial genitive. Replaced O.E. æne.
Spelling changed as pronunciation shifted from two syllables to one after c.1300. Pronunciation change to "wuns" parallels that of one
. As an emphatic, meaning "once and for all," it is attested from c.1300, but this now is regarded as a Pennsylvania German dialect formation. Meaning "in a past time" (but not necessarily just one time) is from c.1250. Once upon a time
as the beginning of a story is recorded from 1595. Slang once-over
"inspection" is from 1915. At once
originally (c.1230) meant "simultaneously," later "in one company" (c.1300), and preserved the sense of "one" in the word; the phrase typically appeared as one word, atones
; the modern meaning "immediately" is attested from 1531.