antagonist

noun
an*tag*o*nist \ an-ˈta-gə-nist \
1555{ds||1||}
  • one that contends with or opposes another : adversary, opponent
  • an agent of physiological antagonism: such as
  • a muscle that contracts with and limits the action of an agonist with which it is paired —called also antagonistic muscle
Powered by Merriam-Webster