1. Nouns in -ō.
a. Feminine: carō, flesh.
2. Nouns in -or.
a. Feminine: arbor, tree.
b. Neuter: aequor, sea; cor, heart; marmor, marble.
3. Nouns in -ōs.
a. Feminine: dōs, dowry.
b. Neuter: ōs (ōris), mouth.
4. Nouns in -er.
a. Feminine: linter, skiff.
b. Neuter: cadāver, corpse; iter, way; tūber, tumor; ūber, udder. Also botanical names in -er; as, acer, maple.
5. Nouns in -ĕs.
a. Feminine: seges, crop.