Looking through a dictionary, I notice that some nouns seem to be both masculine and feminine, and not just the ones where it would be obvious from the subject. E.g. Addewid is given as masc or fem (in the Modern Welsh Dictionary).
Is there a grammatical (or semantic) reason for this, or can you just choose a gender in these cases?
Usually when a word can take both genders, this is just because of regional differences and speaker preference.
The only exception (that I know) is the word gwaith, which is male when used as work, but female when used as times (as in unwaith, weithiau and so on)
Thanks, Hendrik – useful to know!
De is another interesting one, which behaves as feminine when it means right and masculine when it means south:
trowch i’r dde (treiglad meddal) = turn to the right
trowch i’r de (dim treiglad) = turn to the south
If anyone is interested (tumbleweed rolls past…) I have just found a nice list of these (there are more!) in section 4.7 (p. 137) of Gramadeg y Gymraeg, Peter Wynn Thomas.