antagonist /antagə″nist/ [Gk, antagonisma, struggle] , 1. one who contends with or is opposed to another. 2. (in physiology) any agent, such as a drug or muscle, that exerts an opposite action to that of another or competes for the same receptor sites. Compare agonist. Kinds include antimetabolite, associated antagonist, direct antagonist, opioid antagonist. 3. (in dentistry) a tooth in the upper jaw that articulates during mastication or occlusion with a tooth in the lower jaw. −antagonistic, adj., −antagonize, v.
