conjugate (v.)

1520s, in the grammatical sense, "inflect (a verb) through all its various forms," from Latin coniugatus, past participle of coniugare "to yoke together," from assimilated form of com "with, together" (see con-) + iugare "to join," from iugum "yoke" (from PIE root *yeug- "to join"). "This use has its origin in the fact that in inflected languages, a verb is conjugated by conjoining certain inflectional syllables with the root" [Century Dictionary]. Earlier as an adjective, "joined together" (late 15c.). Related: Conjugated; conjugating.