Rancid/ˈrænsɪd/ Definition 1 of 2Pro Tip 1/3Identifying Spoilage Use 'rancid' to describe foods with fats or oils that have gone bad, primarily from smell or taste. The rancid nuts left a bad taste in my mouth. Pro Tip 2/3Not Just Smell 'Rancid' can also describe a stale taste, not just smell, which is important in food quality. These chips taste rancid; they must be old. Pro Tip 3/3Safety Cue Describing food as 'rancid' is a warning that it may be unsafe to eat, as it is likely spoiled. This rancid chicken could make someone sick.