The term 'Singer, of a Sort' can be broken down into two crossword solutions: RAT (3 letters) and STOOLIE (7 letters). A RAT is an informer or spy who betrays their friends or colleagues by providing information to the authorities. A STOOLIE is someone who provides information to the police or other law enforcement agencies, usually in exchange for money or other favors. Both terms refer to people who provide information to the authorities, but a RAT is more commonly used to refer to someone who does so out of personal gain, while a STOOLIE is more often used to refer to someone who does so out of loyalty or obligation.