The term 'TURN BAD' can be broken down into four crossword solutions: ROT (3 letters), SOUR (4 letters), SPOIL (5 letters), and GOSOUTH (7 letters). ROT is a verb meaning to decay or decompose, usually due to the action of bacteria or fungi. SOUR is an adjective meaning having an acidic, sharp, or tangy taste. SPOIL is a verb meaning to damage or impair the quality or value of something. GOSOUTH is an idiom meaning to deteriorate or decline. Together, these words describe the process of something going from good to bad.