sick·ness noun (-es) Etymology: Middle English siknesse, seknesse, from Old English sēocnesse, from sēoc sick + -nesse -ness — more at sick 1. a.: the condition of being ill : ill health : illness b.: a disordered, weakened, or unsound condition < a sickness of judgment would seem to be easily recognizable — Cross Currents > 2. a.: a form of disease : malady b.: menses 3. a.: nausea, queasiness < sickness of stomach > — see motion sickness b.: vomit