I'm curious as to how to say "interrogative mood" in Latin. Is it modus interrogativum?
Were it such a thing, it would be modus interrogativus, since modus is masculine.
Lewis & Short II.B.3 contains the examples for using modus as a classification for verbs:
- In gram., a form of a verb, a voice or mood: “in verbo fiunt soloecismi per genera, tempora, personas, modos, etc.,” Quint. 1, 5, 41: patiendi modus (the passive voice) ... faciendi modus (the active voice), id. 9, 3, 7; cf. 1, 6, 26.