roach1 / rōch/ • n. inf. 1. a cockroach.2. the butt of a marijuana cigarette.roach2 • n. (pl. same) an edible Eurasian freshwater fish (Rutilus rutilus) of the minnow family, popular with anglers. It can hybridize with related fishes, notably rudd and bream.roach3 • n. Sailing a curve, in or out, in the edge of a sail, esp. in the leech of a fore-and-aft sail.