Entry 1 sense Webster, 1913 Cantharidal /(kăn*thăr"ĭ*dal)/ · Can·thar·i·dal · IPA 01 a. Of or pertaining to cantharides or made of cantharides; as, cantharidal plaster. 1. Of or pertaining to cantharides or made of cantharides; as, cantharidal plaster.