Fervent /fərvənt/ / adj. 

Definition:  The word fervent means to have or display a passionate intensity. In antiquity, the word was used to mean “hot, burning, or glowing.” 

Etymology:  The word made its way into the English language during the time of Middle English, which spanned from after the Norman conquest until the late fifteenth century. Its usage during Middle English can be traced back to Old French, which itself can be further traced back to the Latin word fervere. Fervere was used in Old French as a verb to mean “boiling.”

In a Sentence

The man was a fervent follower of Christianity, having religiously devoted himself in his youth.

Many political topics of concern lead to fervent discussions amongst those of opposing positions.

We are fervently hoping for a peaceful solution, wanting to avoid additional conflict as much as possible.

Fans of the supergroup BTS are known for their fervent and unwavering support for the members, their music, and their goals.

Synonyms

Passionate, Intense, Zealous, Spirited, Avid, Devout 

Antonyms 

Apathetic, Dull, Unenthusiastic, Dispassionate, Indifferent, Unconcerned