lest

in order to prevent something bad from happening; so that something bad does not happen

para que no, por si acaso

• lest somebody/something + verb

Collocations take precautions lest something happens · be prepared lest there is a problem

• We must be careful to lock the door, lest someone breaks in.

  Debemos tener cuidado de cerrar la puerta, por si alguien entra.