The definition of avaunt is to be gone, leave or depart.(interjection)
An example of avaunt is what a king would say to a servant to dismiss him from the room.
See avaunt in Webster's New World College Dictionary
Origin: ME < OFr avant, forward < LL abante < L ab, from + ante, before
See avaunt in American Heritage Dictionary 4
Origin: Middle English, forward
Origin: , from Old French avant
Origin: , from Latin abante
Origin: : ab-, from; see ab-1
Origin: + ante, before; see ante-.