late 14c. (early 14c. in Anglo-French), from Old French grané (with -n- misread for -u- -- the character used for -v- in medial positions in words in medieval manuscripts) "sauce, stew," probably originally "properly grained, seasoned," from Latin granum "grain, seed" (see corn, n.1). See discussion in OED. Meaning "money easily acquired" first attested 1910; gravy train (1927) was originally railroad slang for a short haul that paid well.