means To stand, sit, or move with a drooping, careless, ungraceful posture — or, as a noun, an inept or lazy person, usually in the phrase 'no slouch.'

from First surfaces in the 1500s meaning a lazy or unkempt person, of uncertain origin but likely Scandinavian — compare Old Norse 'slokr,' a lazy fellow, part of a whole family of 'sl-' words in English (slack, slug, sluggard, slump) that all seem to sag and droop by sound alone. The bodily sense — the caved chest and rounded shoulders — came later, the posture growing out of the person.