oneyoudaoicibaDictYouDict[one 词源字典]
one: [OE] One is the English member of an ancient and widespread family of ‘one’-words that goes back ultimately to Indo-European *oinos. This also produced Latin ūnus (ancestor of French un and Italian and Spanish uno and source of English ounce, union, unit, etc), Welsh un, Lithuanian víenas, Czech and Polish jeden, and Russian odin, all meaning ‘one’.

Its Germanic descendant was *ainaz, which has fanned out into German ein, Dutch een, Swedish and Danish en, and English one. In many languages the word is used as the indefinite article, but in English the numeral one has become differentiated from the article a, an. One lies behind alone, atone, and only (all of which preserve its earlier diphthongal pronunciation) as well as once, and its negative form is none.

The use of the word as an indefinite pronoun, denoting ‘people in general’, dates from the late 15th century.
=> alone, atone, eleven, inch, lonely, none, once, only, ounce, union, unit[one etymology, one origin, 英语词源]
one (n.)youdaoicibaDictYouDict
c. 1200, from Old English an (adjective, pronoun, noun) "one," from Proto-Germanic *ainaz (cognates: Old Norse einn, Danish een, Old Frisian an, Dutch een, German ein, Gothic ains), from PIE *oi-no- "one, unique" (cognates: Greek oinos "ace (on dice);" Latin unus "one;" Old Persian aivam; Old Church Slavonic -inu, ino-; Lithuanian vienas; Old Irish oin; Breton un "one").

Originally pronounced as it still is in only, and in dialectal good 'un, young 'un, etc.; the now-standard pronunciation "wun" began c. 14c. in southwest and west England (Tyndale, a Gloucester man, spells it won in his Bible translation), and it began to be general 18c. Use as indefinite pronoun influenced by unrelated French on and Latin homo.

One and only "sweetheart" is from 1906. One of those things "unpredictable occurrence" is from 1934. Slang one-arm bandit "a type of slot machine" is recorded by 1938. One-night stand is 1880 in performance sense; 1963 in sexual sense. One of the boys "ordinary amiable fellow" is from 1893. One-track mind is from 1927. Drinking expression one for the road is from 1950 (as a song title).