He paused, afraid lest he say too much. She worried lest he should tell someone what had happened.lestlest /lest/ ●○○ conjunction literary 
She turned away from the window lest anyone see them.2used to show that someone is afraid or worried that a particular thing might happenworried/concerned/anxious etc lest ... He paused, afraid lest he say too much. She worried lest he should tell someone what had happened.
WORD ORIGINlest
Origin:
Old English thy læs the ‘by which less that’EXAMPLES FROM OTHER DICTIONARIES
- He paused, afraid lest he say too much.
- She pulled away from the window lest anyone see them.
COLLOCATIONS FROM THE ENTRY He paused, afraid lest he say too much. She worried lest he should tell someone what had happened.
1in order to make sure that something will not happen: He paused, afraid lest he say too much. She worried lest he should tell someone what had happened. She turned away from the window lest anyone see them.2used to show that someone is afraid or worried that a particular thing might happenworried/concerned/anxious etc lest ... He paused, afraid lest he say too much. She worried lest he should tell someone what had happened.