1. A person who actively opposes or is hostile to someone or something; an adversary
The antagonist in the novel plots against the protagonist.
O antagonista no romance faz planos contra o protagonista.
2. In biology/pharmacology, a substance that interferes with or inhibits the physiological action of another
The drug acts as a dopamine antagonist in the brain.
O medicamento funciona como um antagonista de dopamina no cérebro.
3. In anatomy, a muscle that opposes the action of another muscle (agonist)
The biceps and triceps are antagonist muscles.
O bíceps e o tríceps são músculos antagonistas.