“This term is a combination of ‘scupper’ (a drain leading water from a low point on a vessel’s deck over its side and into the sea, which- when plugged or stopped- can contain stagnant, foul-smelling liquid and pieces of scummy trash) and ‘lout’ (a doltish, oafish idiot).”
Definition courtesy of:
Choundas, George. The Pirate Primer: Mastering the Language of Swashbucklers and Rogues. Chicago: Writer’s Digest Books, 2007. 231.