quadriceps UK /ˈkwɒd.ɹɪ.sɛps/US /ˈkwɑːd.ɹəˌsɛps/ noun1 •A muscle having four heads, especially the large extensor at the front of the thigh.Lanctot slipped the tourniquet around the other, just under his groin, and twisted it tight, clamping quadriceps and hamstring hard to bone. — 2021 formsquadricepses