I. noun 1. a person who actively opposes or is hostile to someone or something; an adversary. • the woman was forcing her antagonist’s face into the mud.
[Biochemistry] a substance which interferes with or inhibits the physiological action of another.
• LSD is a serotonin antagonist.
Compare with agonist.
[Anatomy] a muscle whose action counteracts that of another specified muscle.Compare with agonist.
– origin late 16th cent.: from French antagoniste or late Latin antagonista, from Greek antagōnistēs, from antagōnizesthai ‘struggle against’ (see antagonize).