sloppy adj.

c. 1400, "mudhole, puddle," probably from Old English -sloppe "dung" (in plant name cusloppe, literally "cow dung"), related to slyppe "slime" (from PIE root *sleubh- "to slide, slip").

The meaning "semi-liquid food" is by 1650s; that of "refuse liquid of any kind, household liquid waste" (usually slops) is from 1815. The meaning "affected or sentimental material" is by 1866.

adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.

late 14c., "loose outer garment" (early 14c. in a surname, sclopmongere), of obscure etymology, perhaps from Old English oferslop "surplice," which seems to be related to Middle Dutch slop, Old Norse sloppr (either of which also might be the source of the Middle English word), perhaps all from Proto-Germanic *slup-, from PIE root *sleubh- "to slide, slip" on the notion of a garment one "slips" on or into (compare sleeve).

The sense was extended generally to "clothing, ready-made clothing" (1660s), usually in plural slops, also a nickname for a tailor. Hence, also, slop-shop "shop where ready-made clothes are sold" (1723).