syn·er·gist / ˈsinərjist/ • n. a substance, organ, or other agent that participates in an effect of synergy.DERIVATIVES: syn·er·gis·tic / ˌsinərˈjistik/ adj.syn·er·gis·ti·cal·ly / ˈˌsinərˈjistik(ə)lē/ adv.

synergist (sin-er-jist) n.
1. a drug that interacts with another to produce increased activity, which is greater than the sum of the effects of the two drugs given separately.

2. a muscle that acts with a prime mover (agonist) in making a particular movement.
—synergism, synergy n. —synergistic (sin-er-jist-ik) adj.