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."
