Word Origin & History
O.E. nigen, from P.Gmc. *niwun (cf. O.Fris. niugun, O.N. niu, Du. negen, Ger. neun, Goth. niun "nine"), from PIE (e)newn (cf. Skt. nava, Avestan nava, Gk. ennea, Alb. nende, L. novem, Lith. devnyi, O.C.S. deveti (the Balto-Slavic forms by dissimilation of -n- to -d-), O.Ir. noin, Welsh naw). Ninth is
O.E. nigonðe. Sense in cloud nine, etc., possibly because, "As the largest one-figure integer, nine is sometimes used for emphasis" [Shipley]. Nine to five "the average workday" is attested from 1959. Nine days has been proverbial since 14c. for the time which a wonder or novelty holds attention. The game of ninepins is attested from 1580.
in phrase to the nines "to perfection" (1787) first attested in Burns, apparently preserves the ancient notion of the perfection of the number as three times three (e.g. the nine Muses, etc.
"[T]he Book of St. Albans, in the sections on blasonry, lays great stress on the nines in which all perfect things (orders of angels, virtues, articles of chivalry, differences of coat armour, etc.) occur." [Weekley]
No one seems to consider that it might be a corruption of to then anes, lit. "for the one (purpose or occasion)," a similar construction to the one that yielded nonce