1640s, a back-formation from pugnacity or else from Latin pugnacis, genitive of pugnax "combative, fond of fighting," from pugnare "to fight," especially with the fists, "contend against," from pugnus "a fist," from PIE *pung-, nasalized form of root *peuk-, *peug- "to stick, stab, to prick" (cognates: Greek pyx "with clenched fist," pygme "fist, boxing," pyktes "boxer;" Latin pungere "to pierce, prick").