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mid-15c., from Latin invitationem (nominative invitatio) "an invitation, incitement, challenge," noun of action from past participle stem of invitare "invite, treat, entertain," originally "be pleasant toward," from in- "toward" (see in- (2)). Second element is obscure; Watkins suggests a suffixed form of root *weie- "to go after something, pursue with vigor," and a connection to English gain (see venison). Meaning "the spoken or written form in which a person is invited" is from 1610s.