The term 'mouth, in slang' can be represented by two crossword solutions: YAP (3 letters) and TRAP (4 letters). YAP is a slang term for talking too much, often used to describe someone who talks incessantly or without thinking. TRAP is a slang term for mouth, usually used to describe someone who talks a lot or speaks without thinking. Both terms are commonly used to describe someone who talks too much or speaks without considering the consequences of their words.