1746, "cross-tempered," probably from the frumps (n.) "bad temper" (1660s) and an earlier verb meaning "to mock, browbeat" (1550s), of obscure origin, perhaps imitative of a sneer or derisive snort. See also frump. Sense of "sour-looking, unfashionable" is from 1825, but this may be a shortening of frumple "to wrinkle, crumple" (late 14c.), from Middle Dutch verrompelen "to wrinkle," from ver- "completely" + rompelen "to rumple." Related: Frumpily; frumpiness.
