"to make less heavy, to lighten a load," mid-14c., lighten, lightnen, from light (adj.1) + -en (1). Figuratively "to make cheerful" from c. 1400. Intransitive sense "become less heavy" is from 1720. Related: Lightened; lightening.

"shed light upon, illuminate, make light or bright," early 14c., from light (n.) + -en (1). Intransitive meaning "to become brighter" is late 14c.; of faces, expressions, etc., from 1795. Meaning "to flash lightning" is from mid-15c. Related: Lightened; lightening.

"the shedding of light," mid-14c., verbal noun from lighten (v.2). Meaning "alleviation of weight" (literal and figurative) is from 1520s, from lighten (v.1).

late 14c., "to remove the dimness or blindness" (usually figurative, from one's eyes or heart); see en- (1) + lighten (v.2). From 1660s as "supply with intellectual light." Literal senses are later and less common in English: "put light in" is from 1580s; "shed light upon" is from 1610s. Related: Enlightened; enlightening. Old English had inlihtan "to illuminate, enlighten."

late 14c., "a rising, height of something, height to which something is elevated," from Old French elevation and directly from Latin elevationem (nominative elevatio) "a lifting up," noun of action from past-participle stem of elevare "lift up, raise," figuratively, "to lighten, alleviate," from ex "out" (see ex-) + levare "to lighten; to raise," from levis "light" in weight (from PIE root *legwh- "not heavy, having little weight"). Meaning "act of elevating" is from 1520s.

late 15c., "to raise above the usual position," from Latin elevatus, past participle of elevare "lift up, raise," figuratively, "to lighten, alleviate," from ex "out" (see ex-) + levare "lighten, raise," from levis "light" in weight (from PIE root *legwh- "not heavy, having little weight"). Sense of "raise in rank or status" is from c. 1500. Moral or intellectual sense is from 1620s. Related: Elevated (which also was old slang for "drunk"); elevating.

"to the purpose, applicable, pertinent to the matter at hand," 1550s, from French relevant "depending upon," originally "helpful," from Medieval Latin relevantem (nominative relevans), from stem of Latin relevare "to lessen, lighten," hence "to help, assist; comfort, console" (see relieve). Not generally used until after 1800.

"rapid attack," 1939, from German Blitzkrieg, from Krieg "war" (see kriegspiel) + Blitz "lightning," from Middle High German blicze, back-formation from bliczen "to flash," from Old High German blecchazzen "to flash, lighten" (8c.), from Proto-Germanic *blikkatjan, from PIE root *bhel- (1) "to shine, flash, burn."

early 15c., alleviaten, "to mitigate, relieve (sorrows, suffering, etc.)," from Late Latin alleviatus, past participle of alleviare "lift up, raise," figuratively "to lighten (a burden), comfort, console," from assimilated form of Latin ad "to" (see ad-) + levis "light" in weight (from PIE root *legwh- "not heavy, having little weight"). Related: Alleviated; alleviating.

also alto-relievo, "a form in relief in which the objects stand out very much from the background," 1717, from Italian, literally "high-relief" in sculpture, from alto "high," from Latin altus (see alti-) + rilievo, from rilevare "to raise," from Latin relevare "to raise, lighten" (see relieve).