The following is a list of nouns that features both a masculine and neuter form, each with the same meaning. Allen and Greenough hint that there are “many others of rare occurrence” beyond this list, suggesting neuter-for-masculine is a comfortable poetic standard, but these are the most common instances, or the ones used most widely in classical literature.
- balteus/um, -ī sword belt, girdle
- cāseus/um, ī cheese (also, in comedy, term of endearment)
- clipeus/um, ī round brazen shield
- collum/us, ī neck
- cingulum/us, ī waistband, waist strap
- pīleus/um, ī liberty cap
- tergum/us, ī back
- vāllum/us, ī wall, rampart
By the way, the Allen and Greenough term for these guys is heterogeneous. This term also covers the plūria transexuālia and plūria aliēna that I discussed in earlier posts.
Latin for Addicts 