lest

conj

Etymology: c. 1200, contracted from Middle English les te (“less that”), from Old English þȳ lǣs þe (“whereby less that”), from þȳ (instrumental case of demonstrative article þæt (“that”)) + lǣs (“less”) + þe (“that,” relative particle). The þȳ was dropped and the remaining two words contracted into leste.

1. For fear that; that not; in order to prevent something from happening; in case.

   “He won't go outside, lest he be eaten by those ravenous eagles.”

   “I brought my notes lest faulty memory lead me astray.”

2. that (without the negative particle; introduces the reason for an emotion.)

   “There was danger/alarm lest the plan become known.”

   “I am afraid lest I revealed too much.”