Large and loose trowsers, from which loose clothing is called slops. The word, says Todd, was formerly used in the singular; as in Chaucer:
His overest slop is not worth a mite.
Slop-clothing is the term now universally applied to ready made clothing for seamen. It was so used in 1691.
The slop-seller is a person crept into the navy, I mean to monopolize the vending of clothing only, but since the restoration of King Charles the Second.--Maydman, Naval Speculat. (1691).