“that which stops,” “instrument for halting,” “agent of arrest” — instrumental/agentive suffix denoting a device that arrests flow
The word entered English in the 1820s as haemostat (noun), borrowed from Modern Latin haemostatus, from Greek αἷμα (haima) + ἵστημι (histēmi) — literally “blood-stopper.” The adjective haemostatic appeared in the 1830s, and haemostasis in the 1720s. The root histēmi (“to stand, to stop”) connects -stat to the entire motion and arrest roots: haemostasis (haima + histēmi → stopping of blood flow), haemostatic (haima + stasis + -tic → tending to arrest bleeding), and myostat (mys + stat → instrument that relaxes/paralyzes muscle fibers by stopping contraction). The instrumental/agentive suffix-stat is productive in surgery, hematology, and pharmacology: e.g., haemostat, myostat, vasostat, osteostat, and cardiostat.