Lest

lest

  /lest/

lest /lɛst/conj (subordinating; takes should or a subjunctive verb)

1. so as to prevent any possibility that: he fled the country lest he be captured and imprisoned
2. (after verbs or phrases expressing fear, worry, anxiety, etc) for fear that; in case: he was alarmed lest she should find out

Etymology: Old English the lǣste, earlier thӯ lǣs the, literally: whereby less that