LSJ
ῶνος, ὁ, the fourth month of the Att. year, named from the festival Πυανόψια, corresponding to the latter part of October and former of November, IG1². 6.64, 2². 1014.4, etc. ; also at Priene, Miletus, etc., SIG 282.19 (iv BC), 588.90 (ii BC), etc. ; freq. written Πυανεψιών, Thphr. HP 4.2.10, etc. ; but not in Att. Inscrr. (exc. Ποιανεψιών IG2². 2239.82 (iii AD)); cf. Κυανοψιών.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)