coordinating conjunction, correlative, 'cause, although, causal, albeit, conjunction, assuming, and, or, and/or, so that, to prevent, in order to avoid.
It is before all things important that youth should be young, lest
it should not know how to be old when age comes upon it.
You have been afraid every day lest
I should begin a second time to press you for an answer, haven't you?
It was a wretched face, but she tried to keep it calm lest
it should plead for her.