vain

• adj.無益な; うぬぼれた; 実りのない; 役に立たない

ラテン語のvanus（空虚な、むなしい）から、PIE*wa-no（分離した、見捨てられた）が語源で、語源的にはvacate（空虚な、欲しい、衰えた）と同じ。

vain

vain: [13] Latin vānus meant ‘empty’ (it was related to vacuus ‘empty’, source of English vacuum). It passed into English via Old French vain in the sense ‘worthless’, and the main modern meaning ‘conceited’ did not develop until the 17th century. Also from vānus come English evanescent, vanish, vanity [13], and vaunt [14], and wane, want, etc go back to the same ultimate Indo-European base.
=> evanescent, vanish, vanity, vaunt, wane, want

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 *wa-no-, from root *eue- "to leave, abandon, give out" (cognates: Old English wanian "to lessen," wan "deficient;" Old Norse vanta "to lack;" Latin vacare "to be empty," vastus "empty, waste;" Avestan va- "lack," Persian vang "empty, poor;" Sanskrit una- "deficient," Armenian unain "empty").

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.

1. He is still vain enough to dye his hair red.

彼はまだ見栄っ張りで、髪を赤褐色に染めた。

2.It became obvious that all her complaints were in vain .

彼女のすべての愚痴が無駄だということは明らかだ。

3.I am not a vain creature.

私は見栄っ張りではありません。

4.She is perceived as vain ，spoilt and promiscuous.

彼女は甘やかされた、見栄っ張りで淫乱な女だと思われている。

5.He was self-important， vain and ignorant.

彼は傲慢で自負し、虚栄で無知である。