The term 'treacherous type' can be described by four crossword solutions: SNAKE (5 letters), VIPER (5 letters), SERPENT (7 letters), and snakeinthegrass (15 letters). All of these words refer to a type of animal that is known for being sly and dangerous. Snakes, vipers, and serpents are all members of the same family of reptiles, and they are often seen as symbols of deceit and betrayal. The phrase 'SNAKE in the grass' is an idiom used to describe someone who is untrustworthy and sneaky.