c. 1300, merveillous, "causing wonder, of wonderful appearance or quality," from Old French merveillos "marvelous, wonderful" (Modern French merveilleux), from merveille (see marvel (n.)). Weakened sense of "splendid, very nice" is by 1924. The adverbial sense of "wonderfully, surprisingly" (early 14c.) is archaic or obsolete. Related: Marvelously; marvelousness.
