aggressor (adg-), ōris, m. [aggredior],
one that attacks , an assailant , aggressor (only in the Lat. of the Pandects), Dig. 29, 5, 1 fin. ; also for a robber , ib. 48, 9, 7 al.
·noun The person who first attacks or makes an aggression; he who begins hostility or a quarrel; an ...
Webster's Dictionary of the English Language