Under this theory the word was influenced by Old French vagant, vagaunt "wandering," from Latin vagantem (nominative vagans), past participle of vagari "to wander, stroll about" (see vagary). But on another theory the Anglo-French word ultimately is from Old French vagant, with an unetymological -r-. Middle English also had vagaunt "wandering, without fixed abode" (late 14c.), from Old French vagant.
"uncertain as to specifics," 1540s, from French vague "empty, vacant; wild, uncultivated; wandering" (13c.), from Latin vagus "strolling, wandering, rambling," figuratively "vacillating, uncertain," perhaps from PIE *Huog-o- and cognate with Old Norse vakka "to stray, hover," Old High German wankon "to totter, stagger," Old High German winkan "to waver, stagger, wink," Old English wincian "to nod" [de Vaan]. Related: Vagueness.
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.