Found 1 definition: avast.
Pos: Interjection
[CIDE DICTIONARY]
avast, interj. [Corrupted from D. houd vast hold fast. See Hold, v. t., and Fast, a.].
Cease; stop; stay. Totten. [1913 Webster]
[OXFORD DICTIONARY]
avast, int. Naut. stop, cease.
Du. houd vast hold fast