Old English clæne "free from dirt or filth, unmixed with foreign or extraneous matter; morally pure, chaste, innocent; open, in the open," of beasts, "not forbidden by ceremonial law to eat," from West Germanic *klainja- "clear, pure" (source also of Old Saxon kleni "dainty, delicate," Old Frisian klene "small," Old High German kleini "delicate, fine, small," German klein "small;" English preserves the original Germanic sense), perhaps from PIE root *gel- "bright, gleaming" (source also of Greek glene "eyeball," Old Irish gel "bright"). But Boutkan doubts the IE etymology and that the "clean" word and the "small" word are the same.

"Largely replaced by clear, pure in the higher senses" [Weekley], but as a verb (mid-15c.) it has largely usurped what once belonged to cleanse. Meaning "whole, entire" is from c. 1300 (clean sweep in the figurative sense is from 1821). Sense of "not lewd" (as in good, clean fun) is from 1867; that of "not carrying anything forbidden" is from 1938; that of "free of drug addiction" is from 1950s. To come clean "confess" is from 1919, American English.

mid-15c., of wine, "muddy, not clear," from Old French impur (13c.), from Latin impurus "not pure, unclean, filthy, foul," from assimilated form of in- "not, opposite of" (see in- (1)) + purus "pure" (see pure).

In English, the subsequent order of sense appearance seems to be "earthly, mundane, not spiritual" (c. 1500); "obscene, lewd, unchaste, immoral" (1530s); "mixed with offensive matter, tainted" (1590s); "mixed or combined with other things" (without reference to foulness), 1620s. As a noun from 1784. Related: Impurely.

mid-15c., "having or intended to show faith in and reverence for the Supreme Being," from Latin pius "dutiful, devout, conscientious, religious; faithful to kindred; inspired by friendship, prompted by natural affections," perhaps [de Vaan, Klein] related to Latin purus "pure, clean," via a PIE *pu-io- "purifying" (see pure), but the exact development is disputed.

The classical Roman sense of "having or exhibiting due respect and affection for parents and others to whom such is due" is attested in English from 1620s. In the religious sense, sometimes denoting practice under pretense of religion or for good ends (1630s) and in this sense often coupled with fraud (n.). Related: Piously; piousness.

"to cause (liquid or granular substance) to flow or stream either out of a vessel or into one," c. 1300, of unknown origin. Not in Old English; perhaps from Old French (Flanders dialect) purer "to sift (grain), pour out (water)," from Latin purare "to purify," from purus "pure" (see pure). Replaced Old English geotan. Intransitive sense of "to flow, issue forth in a stream" is from 1530s. Related: Poured; pouring; pourable. As a noun from 1790, "a pouring stream."

c. 1300, pur blind "entirely blind," as a noun, "a blind person," later "partially blind, blind in one eye" (late 14c.), the main modern sense, from blind (adj.) + pur "entirely, completely, absolutely."

The adverb forming the first element is from an identical Middle English adjective pur "unadulterated, unmixed" (c. 1300), usually explained as from Old French pur and Latin purus (see pure). It might have been influenced by the Anglo-French perfective prefix pur- (see pur-). The sense of "dull" is recorded from 1530s.

also pure-blood, "of unmixed inheritance or ancestry," 1851, from pure blood (n.), attested from 1751 in reference to breeding, from pure (adj.), which is attested from late 15c. in reference to unmixed descent or lineage, + blood (n.). As a noun meaning "a pure-blood animal" from 1882.

also pure-bred, "of unmixed inheritance or ancestry," 1868, from pure (adj.) + bred.

c. 1300, pureli, "wholly, fully, completely; actually, really, truly," from pure + -ly (2). Sense of "without physical admixture" is from c. 1500.

late 14c., purenes, purenesse, "freedom from admixture or defilement; spiritual or moral purity," from pure (adj.) + -ness.

c. 1300, purgen, "clear of a charge or suspicion," from Anglo-French purger, Old French purgier "wash, clean; refine, purify" morally or physically (12c., Modern French purger) and directly from Latin purgare "cleanse, make clean; purify," especially in reference to the body, "free from what is superfluous; remove, clear away," but also figuratively "refute, justify, vindicate," from Old Latin purigare, from purus "pure" (see pure) + root of agere "to set in motion, drive; to do, perform" (from PIE root *ag- "to drive, draw out or forth, move").

By mid-14c. as "to cleanse (a person or soul) from sin or moral defilement; to cleanse, clear, purify" (metal, etc.), also medicinally "to cleanse the body or digestive tract by a laxative, diuretic, or emetic." The figurative sense of "make ideal or pure, rid of objectionable elements or members" is by 1580s. Related: Purged; purging. The Latin verb is also the source of Spanish purgar, Italian purgare.