The term 'treacherous one' can be described by a variety of words, all of which have seven or fewer letters. The first is 'DASTARD, ' which means a person who is cowardly and treacherous. The second is 'SNAKE, ' which is a reptile known for its slyness and cunning. The third is 'VIPER, ' which is a type of SNAKE known for its venomous bite. The fourth is 'SERPENT, ' which is another word for SNAKE. The fifth is 'RAT, ' which is an animal known for its deceitful behavior. The sixth is 'snakeinthegrass, ' which is an idiom meaning someone who is sly and untrustworthy. The seventh is 'awolfinsheepsclothing, ' which is another idiom meaning someone who appears to be harmless but is actually dangerous.