Identify the correct meaning of the given word-
Lest
a) Unless
b) But
c) Fear
d) All

Hint:
The dictionary meaning of the given word “lest” is “with the intention of prevention to avoid the risk”. For example, He spent whole days in his room, wearing headphones lest he disturbs anyone.

Complete answer:
In English, lest is used for fear that – used when you are saying something in order to prevent something from happening. It is used for fear that; in case of; so that, etc. It is a conjunction. For example, He kept his notes by his side lest faulty memory leads him astray.
Now, let us examine all the given options to find out the correct answer :
Option ‘a’ is Unless. It is also a conjunction. It means – except if (used to introduce the case in which a statement made is not true or valid). For example: Unless you have a photographic memory, reputation is vital.
Option ‘b’ is But. It is conjunction as well. It is used to introduce a phrase or clause contrasting with what has already been mentioned. For example, He stumbled but didn’t fall.
Option ‘c’ is Fear. It is a noun. It is an unpleasant opinion caused by a threat of danger, pain, or harm. For example, A covered in fear as bullets whizzed past.
Option ‘d’ is All. It is pre-determiner. It is used to refer to the whole quantity or extent of a particular group of things. For example All the people I met.
As we have examined all the given options, we can easily figure out the correct answer. Here, the correct meaning of the given word “lest” is “but”.
So, the correct answer is “Option b”.

Note:
 Don’t get confused between “fear” and “but” as there is “fear” mentioned in the definition of “lest”. Here, you have to find another word with the same kind of usage as “but”, and not “fear”.