Etymology
Advertisement
only (adj.)

"single as regards number, class, or kind," Middle English onli, from Old English ænlic, anlic "only, unique, solitary," literally "one-like," from an "one" (see one) + -lic "-like" (see -ly (1)). Similar formation in Old Frisian einlik, Dutch eenlijk, Old High German einlih, Danish einlig. It preserves the old pronunciation of one. Related: Onliness.

Its use as an adverb ("alone, no other or others than; in but one manner; for but one purpose") and conjunction ("but, except") developed in Middle English. Distinction of only and alone (now usually in reference to emotional states) is unusual; in many languages the same word serves for both. German also has a distinction in allein/einzig. Phrase only-begotten (mid-15c.) is biblical, translating Latin unigenitus, Greek monogenes; the Old English word was ancenned. Only child is attested by 1700.

Related entries & more 
Advertisement
one (adj., pron., n.)

"being but a single unit or individual; being a single person, thing, etc. of the class mentioned;" as a pronoun, "a single person or thing, an individual, somebody;" as a noun, "the first or lowest of the cardinal numerals; single in kind, the same; the first whole number, consisting of a single unit; unity; the symbol representing one or unity;" c. 1200, from Old English an (adjective, pronoun, noun) "one," from Proto-Germanic *ainaz (source also of Old Norse einn, Danish een, Old Frisian an, Dutch een, German ein, Gothic ains), from PIE root *oi-no- "one, unique."

Originally pronounced as it still is in only, atone, alone, 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. Its use as indefinite pronoun was influenced by unrelated French on and Latin homo.

Before the name of a person, indicating "hitherto unknown" or not known to the speaker.

One and only "sweetheart" is from 1906. Slang one-arm bandit for 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 "mind capable of only one line of thought or action" is by 1915. Drinking expression one for the road is from 1950 (as a song title). One-man band is by 1909 in a literal sense, 1914 figurative. One of those things "unpredictable occurrence" is from 1934 (Cole Porter's song is from 1935).

The conscience clause is one of the weaknesses of the Bill. It is one of those things which tend to create the bitterness. The conscience clause is one of those things which are inseparable from a Bill like this. It is one of those things which divides the sheep from the goats—members can pick them out for themselves—in the playground, in the school. ["Religious Exercises in School Bills," New Zealand Parliamentary Debates, Aug. 13, 1926]
Related entries & more 
sole (adj.)
"single, alone, having no husband or wife; one and only, singular, unique," late 14c., from Old French soul "only, alone, just," from Latin solus "alone, only, single, sole; forsaken; extraordinary," of unknown origin, perhaps related to se "oneself," from PIE reflexive root *swo- (see so).
Related entries & more 
hang-dog (adj.)
also hangdog, 1670s, apparently "befitting a hang-dog," that is, a despicable, degraded fellow, so called either from being fit only to hang a dog (with construction as in cutthroat, daredevil) or of being a low person (i.e. dog) fit only for hanging. The noun, however, is attested only from 1680s.
Related entries & more 
monogamy (n.)

1610s, "practice of marrying only once in a lifetime," from French monogamie, from Late Latin monogamia, from Greek monogamia "single marriage," from monogamos "marrying only once," from monos "single, alone" (from PIE root *men- (4) "small, isolated") + gamos "marriage" (see gamete). As "condition of being married to only one person at a time," by 1708.

Related entries & more 
Advertisement
SRO 
1941, initialism (acronym) for standing room only.
Related entries & more 
turnkey (adj.)
1650s, "jailer," from turn (v.) + key (n.). In reference to a job that only has to be done only once, it is recorded from 1934. The notion probably is of something that can be accomplished with a single turn of a key.
Related entries & more 
hireling (n.)
"one who works for hire," Old English hyrling; see hire (v.) + -ling. Now only disparaging, "one who acts only for mercenary motives," a sense that emerged late 16c. As an adjective by 1580s.
Related entries & more 
atween (adv.)
"between," c. 1400, from a- (1) + tween. Now obsolete or only Scottish.
Related entries & more 
hapax legomenon (n.)
(plural legomena), "word occurring only once," Greek, literally "once said," from hapax "once only" + legomenon, neuter passive present participle of legein "to say," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."
Related entries & more