Entry 1 sense Webster, 1913 Rancid /(răn"sĭd)/ · Ran·cid · IPA /ˈɹænsɪd/ 01 a. Having a rank smell or taste, from chemical change or decomposition; musty; as, rancid oil or butter. 1. Having a rank smell or taste, from chemical change or decomposition; musty; as, rancid oil or butter.