nine (adj., n.)

"the cardinal number one more than eight or one less than ten; the number which is one more than eight;" Middle English nīn, from Old English nigen, from Proto-Germanic *newun (source also of Old Saxon nigun, Old Frisian niugun, Old Norse niu, Swedish nio, Middle Dutch neghen, Dutch negen, Old High German niun, German neun, Gothic niun "nine").

This is from PIE root *newn "nine" (source also of Sanskrit nava, Avestan nava, Greek ennea (with unetymological initial e-), Albanian nende, Latin novem (with change of -n- to -m- by analogy of septem, decem), Lithuanian devyni, Old Church Slavonic deveti (the Balto-Slavic forms by dissimilation of -n- to -d-), Old Irish noin, Welsh naw).

As "a symbol representing the number nine," late 14c. The proverbial nine lives of a cat are attested from 17c.  Nine-to-five "the average workday" is attested from 1935. Nine days (or nights) has been proverbial since mid-14c. for the time which a wonder or novelty holds attention; the expression nine days' wonder is from 1590s. The Nine "the Muses" is from c. 1600. Also see nines.

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Definitions of nine from WordNet
nine (n.)
the cardinal number that is the sum of eight and one;
Synonyms: " / ix / niner / Nina from Carolina / ennead
nine (n.)
a team of professional baseball players who play and travel together;
Synonyms: baseball club / ball club / club
nine (n.)
one of four playing cards in a deck with nine pips on the face;
Synonyms: nine-spot
nine (adj.)
denoting a quantity consisting of one more than eight and one less than ten;
Synonyms: " / ix