1300-50;Middle Englishmastif, perhaps extracted from Anglo-Frenchmasti(n)s (taken as *mastifs), plural of Old Frenchmastin < Vulgar Latin (canis) *ma(n)suētīnus, derivative of Latinmansuētus tame, mild (see mansuetude)
"large, powerful breed of dog," early 14c., from O.Fr. mastin or Prov. mastis, both from V.L. *mansuetinus "domesticated," from L. mansuetus "tame, gentle" (see mansuetude). Form influenced by O.Fr. mestif "mongrel."