From Latin 'evanescere' (to become empty), from 'vanus' (empty) — kin to 'vain,' 'vanity,' and 'vacant.'
To disappear suddenly and completely; to cease to exist.
From Old French evaniss-, the extended stem of evanir (to vanish, to disappear), from Vulgar Latin *exvanīre, a remodelled form of Latin ēvānēscere (to vanish, to pass away, to dissipate), from ex- (out, away) + vānēscere (to become empty, an inceptive verb from vānus, empty, void, hollow). The Latin vānus derives from PIE *h₁weh₂- (empty, lacking, vain), also underlying Latin vacuus (empty), vacare (to be empty, to be free — whence vacant and vacation), and vanity. To vanish is therefore literally to become empty — to drain away into void. The Middle English
'Vanish,' 'vain,' 'vanity,' and 'vacant' all come from Latin 'vānus' (empty). A vain person is etymologically 'empty,' vanity is 'emptiness,' and to vanish is 'to become empty' — the entire cluster revolves around the concept of hollowness and nothingness.