lest
conjunction /lest/
/lest/
(formal or literary)- in order to prevent something from happening
- He gripped his brother's arm lest he be trampled by the mob.
- Lest anyone should doubt my story, I have brought documents to attest to its truth.
- used to introduce the reason for the particular emotion mentioned
- She was afraid lest she had revealed too much.
Word OriginOld English thȳ lǣs the ‘whereby less that’, later the læste.