The phrase "play Judas" is a reference to the character named Judas in the Bible, who betrayed Jesus for 30 pieces of silver. The phrase is often used to describe someone who betrays someone else for personal gain, usually in a treacherous manner. There are many synonyms for this phrase, including "backstab," "double-cross," "sell out," "treachery," "betrayal," and "stab in the back." All of these terms suggest that the betrayer pretended to be loyal but ultimately acted against the person they were supposed to be supporting, often causing significant harm and damage to the victim. Those who "play Judas" are often viewed with contempt and are not trusted by others.