slippery slope

noun

1. a dangerous and irreversible course.

   the slippery slope from narcotics to prison.

Word History and Origins

Origin of slippery slope¹

First recorded in 1985–90

Idioms and Phrases

A dangerous course, one that leads easily to catastrophe, as in He's on a slippery slope, compromising his values to please both the bosses and the union. This metaphoric expression alludes to traversing a slick hillside, in constant danger of falling. [Mid-1900s]