Reading a book from 1995, I encountered the word lest in the proof of a theorem. I had not seen it in about twenty years of reading and working on mathematical contexts. Is this word used nowadays? Babylon suggested to use "against the possibility" instead of it but I found it very easy and beautiful. Did this online software suggest me correctly?
It's a conjunction mostly used in formal documents. The word originally comes from old English and means to prevent something undesirable from happening and in case.
She tiptoed lest her mother should hear her. Meaning in order to prevent here.
She worried lest she should be late. Meaning in case here.
A good alternative is in order to prevent and in case both used in different contexts.
Examples source Wordweb.