snake in the grass

noun

1. a treacherous person, especially one who feigns friendship.

2. a concealed danger.

Word History and Origins

Origin of snake in the grass¹

First recorded in 1690–1700

Idioms and Phrases

A treacherous person, as in Ben secretly applied for the same job as his best friend; no one knew he was such a snake in the grass. This metaphor for treachery, alluding to a poisonous snake concealed in tall grass, was used in 37 b.c. by the Roman poet Virgil (latet anguis in herba). It was first recorded in English in 1696 as the title of a book by Charles Leslie.