Answer: tanist

AnswerCrossword Clue
TANISTCeltic lord.
TANISTIrish lord of yore
TANISTIrish heir-apparent
TANISTAncient Irish chief's heir
tanistthe heir apparent to a Celtic chief
tanistthe successor apparent to a Celtic chief, usually the oldest or worthiest of his kin, chosen by election among the tribe during the chief's lifetime