1727, "muddy," from slop, n.1 + -y(2). Meaning "loose, ill-fitting, slovenly" is first recorded 1825, influenced by slop, n.2. Related: Sloppily; sloppiness. Sloppy Joe was originally "loose-fitting sweater worn by girls" (1942); as a name for a kind of spiced hamburger, it is attested from 1961.