Big-mouth is a term used to describe someone who talks excessively or is unable to keep a secret. There are several synonyms for this word that can be used depending on the situation or context. One such word is blabbermouth, which refers to someone who talks excessively or divulges secrets. Another synonym is chatterbox, which describes someone who talks continuously and usually without much substance. A third synonym is gossipmonger, which applies to someone who spreads rumors or talks about other people's affairs. Other synonyms for big-mouth include windbag, chatterer, loquacious, and motormouth. Overall, these synonyms can be used interchangeably with big-mouth to describe individuals who talk too much or cannot keep their mouths shut.