fanaticism

As a noun fanaticism

is the characteristic or practice of being a fanatic.

As a verb fanaticise is

.

As nouns the difference between interest and fanaticism

is that interest is the price paid for obtaining, or price received for providing, money or goods in a credit transaction, calculated as a fraction of the amount or value of what was borrowed while fanaticism is the characteristic or practice of being a fanatic.

As a verb interest

is to engage the attention of; to awaken interest in; to excite emotion or passion in, in behalf of a person or thing.