conjugation (n.)

mid-15c., "the inflection of a verb in all its different forms; a class of verbs similarly conjugated," from Latin coniugationem (nominative coniugatio), literally "a combining, connecting," noun of action from past-participle stem of coniugare "to join together," from assimilated form of com "with, together" (see con-) + iugare "to join," from iugum "yoke" (from PIE root *yeug- "to join"). Meaning "act of uniting or combining" is from c. 1600.