alieniloquy
/ˌeɪlɪəˈnɪləkwi/rare (literary in later use)
noun
An instance of straying from the subject one is supposed to be talking about; rambling or evasive talk.
Origin
Early 18th century; earliest use found in Nathan Bailey (d. 1742), lexicographer and schoolmaster. From post-classical Latin alieniloquium allegory (636 in Isidore) from classical Latin aliēnus + -loquium, after Hellenistic Greek ἀλληγορία.