a viper in (one's) bosom

a viper in (one's) bosom

A friend, lover, or relation who proves to be traitorous, untrustworthy, deceitful, or ungrateful. (Used especially in the phrase "nourish/nurse/nurture a viper in one's bosom.") Well, it turns out that Margaret was quite a viper in my bosom. I put my neck on the line to get her a job in our company, and then she turns around and tries to steal my position!
See also: bosom, viper
Farlex Dictionary of Idioms.

viper in one's bosom

Also, snake in one's bosom. An ungrateful or treacherous friend, as in I got him dozens of freelance jobs, and then he told everyone I was a lousy musician-nothing like nourishing a viper in one's bosom . This metaphoric expression, often put as nourish a viper (or snake) in one's bosom, comes from Aesop's fable about a farmer who shelters a snake dying from the cold, which then fatally bites him after it recovers. It was referred to by Chaucer and Shakespeare, and appeared in numerous proverb collections.
See also: bosom, viper
The American Heritage® Dictionary of Idioms by Christine Ammer.

a viper in your bosom

a person you have helped but who behaves treacherously towards you.
The phrase comes from one of Aesop's fables, in which a viper reared in a person's bosom eventually bites its nurturer. The idea is also found in Latin (in sinu viperam habere ) and the expression appears in various forms in English from the late 16th century.
See also: bosom, viper
Farlex Partner Idioms Dictionary
See also:
  • a viper in your bosom
  • viper
  • viper in one's bosom
  • a serpent in (one's) bosom
  • a snake in (one's) bosom
  • serpent
  • nourish a viper in (one's) bosom
  • nurse a serpent in (one's) bosom
  • nurture a serpent in (one's) bosom
  • nurture a snake in (one's) bosom