The Collaborative International Dictionary of English v.0.48:
ain \ain\ adj.
   1. belonging to or on behalf of a specified person especially
      one's self; preceded by a possessive. `my ain' is Scottish
   Syn: own(prenominal).
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
ain
    adj 1: belonging to or on behalf of a specified person
           (especially yourself); preceded by a possessive; "for
           your own use"; "do your own thing"; "she makes her own
           clothes"; "`ain' is Scottish" [syn: own(a), ain]
V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):
AIN
       Advanced Intelligent Network (IN)
V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):
AIN
       Auto Insert Notification (CD-R)
Hitchcock's Bible Names Dictionary (late 1800's):
Ain, same as Aiath