1560s, "easily crumbled;" 1570s, "like bread," from crumb + -y (2). Slang meaning "shoddy, filthy, inferior, poorly made" was in use by 1859, probably from the first sense, but influenced by crumb in its slang sense of "louse." The "like bread" sense probably accounts for 18c. (and later in dialects) use, of a woman, "attractively plump, full-figured, buxom." Related: Crummily; crumminess.