Sluggishness rhymes with:
bearishness, boorishness, bullishness, foolishness, jewishness, selfishness, skittishness, squeamishness, waterishness, bearishness, boorishness, brashness, bullishness, foolishness, freshness, harshness, jewishness, selfishness, skittishness, squeamishness, waterishness
Sluggishness sounds like:
salesman's, salesmen's, silicones, siliconix, slackening, slackens, slackness, slashing, slicing, slocan's, slogans, slogging, sloshing, slouching, slugging, sluicing, socializing, squelching, sulking