[571]. Imparisyllables in -es or -ēs and substantives in -er, -ō, -or, and -ōs are masculine: as,
caespes, sod; pēs, foot; agger, mound; sermō, speech; pallor, paleness; flōs, flower.
[572]. These imparisyllables in -es or -ēs are feminine: merges, sheaf, seges, crop, teges, mat; requiēs and quiēs, rest; compedēs, plural, fetters; mercēs, reward. aes, copper, bronze, is neuter.
[573]. These substantives in -er are neuter: cadāver, corpse, iter, way, tūber, swelling, truffle, ūber, udder, verberis, lash, genitive, no nominative; also names of plants in -er: as, acer, maple, cicer, chickpea, papāver, poppy, piper, pepper, siler, osier, siser, skirret, sūber, corktree. linter, tub, boat, is feminine, once masculine. vēr, spring, is neuter.
[574]. Substantives in -ō, with genitive -inis ([485]), are feminine; as, imāgō, imāginis, likeness; also carō, carnis, flesh, and words of action in -iō and -tiō ([227], [228]). But cardō, hinge, ōrdō, rank, and turbō, whirlwind, are masculine. margō, brink, and cupīdō, desire, are sometimes masculine.
[575]. These substantives in -or are neuter: ador, spelt, aequor, sea, marmor, marble, cor, heart. arbor, tree, is feminine.
[576]. These substantives in -ōs are feminine: cōs, whetstone, arbōs, tree, dōs, dowry. ōs, ōris, mouth, face, is neuter, also os, ossis, bone.
FEMININE.
[577]. Parisyllables in -ēs, and substantives in -ās, -aus, -is, -s preceded by a consonant, and -x, are feminine: as,
nūbēs, cloud; aetās, age; laus, praise; nāvis, ship; urbs, city; pāx, peace.