Rancidness refers to the unpleasant, foul taste or smell of something that has gone bad or spoiled. Synonyms for rancidness include putridness, foulness, rankness, staleness, sourness, and mustiness. These words describe the unpleasant and unappetizing state of food that has become inedible due to bacterial growth or oxidation. Additionally, some other synonyms for rancidness could be moldiness, rottenness, decay, or decomposition. These words can also be used to describe the bad odor or taste caused by decaying organic matter. It is important to properly store food to prevent rancidness and dispose of it if it has gone bad.