Entry 1 sense Webster, 1913 Sickening /sĭk'-ən-ĭng/ · Sick·en·ing · IPA /ˈsɪk(ə)nɪŋ/ 01 a. Causing sickness; specif., causing surfeit or disgust; nauseating. 1. Causing sickness; specif., causing surfeit or disgust; nauseating.