1570s, "wearing slippers or loose shoes so that the sole trails after the foot;" see slip (v.) + shod "wearing shoes." The sense of "slovenly, careless" is by 1815, probably from the notion of appearing like one in slippers, or whose shoes are down at the heels. Slipalong (adj.) in the "wearing loose shoes" sense is by 1849.
updated on January 11, 2023