The term 'TURN RANCID' is used to describe the process of food or other organic matter becoming spoiled or rotten. The crossword solutions for this term are SPOIL (5 letters) and ROT (3 letters). SPOIL means to go bad or become inedible, while ROT means to decay or decompose. Both terms refer to the same process of food or other organic matter becoming inedible due to age or exposure to bacteria or other microorganisms.