1. (noun) the principal character in a work of fiction

• protagonist

1. (noun) someone involved in a contest or battle (as in an agon)

• contestant

2. (noun) a muscle that contracts while another relaxes

• antagonistic muscle

3. (noun) (biochemistry) a drug that can combine with a receptor on a cell to produce a physiological reaction

• drug

1. (noun) the principal character in a work of fiction

• antihero

1. (noun) (biochemistry) a drug that can combine with a receptor on a cell to produce a physiological reaction

• biochemistry

1. (noun) someone involved in a contest or battle (as in an agon)

• adversary
• antagonist
• opponent
• opposer
• resister

1. (noun) the principal character in a work of fiction

• agony
• torment
• torture

2. (noun) someone involved in a contest or battle (as in an agon)

• agonistic
• agony
• torment
• torture
• agony
• excruciation
• suffering