used to refer to a large number of something, typically used in an indefinite sense

काफी

English Usage: Many an hour was spent building the sandcastle.

Hindi Usage: काफी घंटे रेत के किले को बनाने में बिताए गए।

indicating a large number of items or people

बहुत सारे

English Usage: Many an student has struggled with the subject.

Hindi Usage: बहुत सारे छात्रों ने इस विषय के साथ संघर्ष किया है।