yellowish-white inflammatory exudation, consisting of white blood cells, etc., produced by suppuration, late 14c., from Latin pus "pus, matter from a sore;" figuratively "bitterness, malice" (related to puter "rotten" and putere "to stink"), from PIE *pu- (2) "to rot, decay" (source also of Sanskrit puyati "rots, stinks," putih "stinking, foul, rotten;" Greek puon "discharge from a sore," pythein "to cause to rot;" Lithuanian pūvu, pūti "to rot;" Gothic fuls, Old English ful "foul"), perhaps originally echoic of a natural exclamation of disgust.

The formation of pus is called suppuration. A collection of pus within the solid tissues is called an abscess. A suppurating open sore is an ulcer. [Century Dictionary]

word-forming element used from mid-19c. and meaning "pus," from Greek puon "pus" (see pus).

"full of pus," from pus (n.) + -y (2). In this sense Middle English had pushi (mid-15c.), from a variant of pus.

early 15c., purulente, "pus-colored," from Latin purulentus "full of pus," from pus (genitive puris) "pus" (see pus). Meaning "consisting of pus" is from 1590s. Related: Purulence.

early 15c., from French suppuration or directly from Latin suppurationem (nominative suppuratio), noun of action from past participle stem of suppurare "form or discharge pus," from sub "under" (see sub-) + stem of pus (see pus).

late 14c., "festering gangrenous, in a state of decay," from Old French putride and directly from Latin putridus, from putrere "to rot," from putris "rotten, crumbling," related to putere "to stink," from PIE root *pu- (2) "to rot, stink" (see pus). First in reference to putrid fever, an old name for typhus (also known in Middle English as putrida), which supposedly was caused by putrefaction of bodily humors. Related: Putridness.

Old English ful "rotten, unclean, vile, corrupt, offensive to the senses," from Proto-Germanic *fulaz (source also of Old Saxon and Old Frisian ful, Middle Dutch voul, Dutch vuil, Old High German fül, German faul, Gothic füls), from PIE *pu- (2) "to rot, decay," perhaps from the sound made in reaction to smelling something bad (see pus).

Old English ful occasionally meant "ugly" (as contrasted with fæger (adj.), modern fair (adj.)), and this sense became frequent in Middle English. The cognate in Swedish is the usual word for "ugly." Of weather from mid-14c. In the sporting sense of "irregular, unfair, contrary to established rule or practice" it is first attested 1797, though foul play is recorded from mid-15c. Baseball sense of "out of play" attested by 1860.

"having relation in the formation of pus," 1835, from pyogenesis, medical Latin; see pyo- "pus" + -genic "producing." Related: Pyogenetic (1855); pyogenesis.

"presence of pus in the urine," 1787, from medical Latin (by 1760s), from pyo- + -uria (see urine).

early 15c., from Latin suppuratus, past participle of suppurare "form or discharge pus" (see suppuration). Related: Suppurated; suppurating.