Etymology
Advertisement
vain (adj.)
c. 1300, "devoid of real value, idle, unprofitable," from Old French vain, vein "worthless, void, invalid, feeble; conceited" (12c.), from Latin vanus "empty, void," figuratively "idle, fruitless," from PIE *wano-, suffixed form of root *eue- "to leave, abandon, give out."

Meaning "conceited, elated with a high opinion of oneself" first recorded 1690s in English; earlier "silly, idle, foolish" (late 14c.). Phrase in vain "to no effect" (c. 1300, after Latin in vanum) preserves the original sense. Related: Vainly; vainness. Compare also vainglory.
Related entries & more 
Advertisement
vainglory (n.)
c. 1200, "worthless glory, undue pomp or show," waynglori, from Old French vaine glorie, from Medieval Latin vana gloria (see vain + glory (n.)).
Related entries & more 
*eue- 
*euə-, Proto-Indo-European root meaning "to leave, abandon, give out," with derivatives meaning "abandoned, lacking, empty."

It forms all or part of: avoid; devastation; devoid; evacuate; evanescent; vacant; vacate; vacation; vacuity; vacuole; vacuous; vacuum; vain; vanish; vanity; vaunt; void; wane; want; wanton; waste.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit una- "deficient;" Avestan va- "lack," Persian vang "empty, poor;" Armenian unain "empty;" Latin vacare "to be empty," vastus "empty, waste," vanus "empty, void," figuratively "idle, fruitless;" Old English wanian "to lessen," wan "deficient;" Old Norse vanta "to lack."
Related entries & more 
vainglorious (adj.)
early 15c., from vainglory + -ous, or from Old French vain glorios "boastful, swaggering." Related: Vaingloriously; vaingloriousness. Grose ("Classical Dictionary of the Vulgar Tongue," 3rd ed., 1796) has vain-glorious man "One who boasts without reason, or, as the canters say, pisses more than he drinks."
Related entries & more 
frothy (adj.)
1530s, "full of foam," from froth + -y (2). Meaning "vain, light, insubstantial" is from 1590s. Related: Frothiness.
Related entries & more 
Advertisement
frustrate (v.)

"make of no avail, bring to nothing, prevent from taking effect or coming to fulfillment," mid-15c., from Latin frustratus, past participle of frustrari "to deceive, disappoint, make vain," from frustra (adv.) "in vain, in error," which is related to fraus "injury, harm," a word of uncertain origin (see fraud). Related: Frustrated; frustrating.

Related entries & more 
frustration (n.)

"act of frustrating, disappointment, defeat," 1550s, from Latin frustrationem (nominative frustratio) "a deception, a disappointment," noun of action from past-participle stem of frustrari "to deceive, disappoint, make vain," from frustra (adv.) "in vain, in error," which is related to fraus "injury, harm," a word of uncertain origin (see fraud). Earlier (mid-15c.) with a now-obsolete sense of "nullification."

Related entries & more 
light-headed (adj.)
also lightheaded, 1530s, "dizzy," from light (adj.1) + -headed. Of persons or actions, "frivolous, vain, thoughtless," from 1570s. Related: Light-headedness.
Related entries & more 
punchless (adj.)

1950 of fighters and others deficient in requisite power, from punch (n.1); 1853 of situations in which one might seek a drink in vain, from punch (n.2). Related: Punchlessly; punchlessness.

Related entries & more 
intramercurial (adj.)
"being within the orbit of the planet Mercury," 1859, especially in reference to a supposed planet orbiting there (sought in vain in the eclipse of 1860), from intra- "within, inside" + Mercury (Latin Mercurius) + -al (1). The idea originated in France in the 1840s with Urbain Le Verrier, who later became director of the Paris Observatory. There was some excitement about it in 1859 when a French doctor named Lescarbault claimed to have tracked it crossing the Sun's disk and convinced Le Verrier. It was sought in vain in the solar eclipses of 1860, '68, and '69. See Vulcan.
Related entries & more