The Allen and Greenough is still under construction;
so some links may not work quite the way you would expect.
Gender in the Third Declension.
84. The Gender of nouns of this declension must be
learned by practice and from the Lexicon. Many are masculine or feminine
by nature or in accordance with the general rules for gender (p. 15).
The most important rules for the others, with their principal exceptions,
are the following: - [Some nouns of doubtful or variable gender are