late 13c., from Anglo-French glorious, Old French glorieus "glorious, blessed" (12c., Modern French glorieux), from Latin gloriosus "full of glory, famous," from gloria (see glory (n.)). In classical Latin and in English late 14c.-17c. it also could mean "boastful, vainglorious." Related: Gloriously; gloriousness. In Middle English with comparative gloriouser, superlative gloriousest.