What's worse, KELEUQOS is neuter in the plural! (in Homer at least: hUGRA
KELEUQA).
The first place I go for help with a question like these nowadays is Andrew
L. Sihler, _New Comparative Grammar of Greek and Latin_. There, on pp.
244-5, #251 ("Gender"), he says:
"In nouns, overt (formal) indications of gender in PIE were few.
For most form-classes, PIE masculine and feminine nouns inflected
identically, and neuter differed from them only in the nominative and
accusative cases. This is true also of i-stem adjectives (a common type)
and interrogative/indefinite pronouns, though as a general rule adjectives
and pronouns are more completely marked for gender than nouns are. Personal
pronouns however have no gender in PIE and in most daughter languages.
"There is one stem-class which is prevailingly masculine and
neuter, the o-stems; and two which are prevailingly feminine, the eH2-
stems (i.e. long-a-stems) and the iH2/yeH2-stems (i.e.
long-i/y-long-a-stema. In both G and L, but unique to them among IE groups,
there are a fair number of feminine o-stems, not formally different from
o-stem masculines in any way ..."
A fact perhaps not unrelated to the above is that compounded adjectives of
the O-declension (e.g. AQANATOS,-ON; EUTUCOS,-ON) never have a distinct
feminine form. But of course this is also true of compound adjectives of
the third declension (that they have no distinct feminine form).
I would note further that apart from the most common nouns you've
mentioned, like hODOS, NHSOS, NOSOS, there are quite a few tree and plant
names that have the O declension but are feminine in gender and must take a
feminine adjective; rightly or wrongly, I've always associated this with
the fact that there are nymphs associated with all trees (dryades) and that
from the Greek perspective, trees really are feminine.
Carl W. Conrad
Department of Classics/Washington University
One Brookings Drive/St. Louis, MO, USA 63130/(314) 935-4018
Home: 7222 Colgate Ave./St. Louis, MO 63130/(314) 726-5649
cwconrad@artsci.wustl.edu OR cconrad@yancey.main.nc.us
WWW: http://www.artsci.wustl.edu/~cwconrad/