passion vs fervency

passion and fervency both are nouns.

Word	Noun	Adjective	Verb	Adverb
passion	Yes	No	No	No
fervency	Yes	No	No	No

As nouns, fervency is a hyponym of passion; that is, fervency is a word with a more specific, narrower meaning than passion:

Other hyponyms of passion include infatuation, abandon, wildness, ardor, ardour, fervidness, fervor, fervour, fire, storminess.

passion (noun)	fervency (noun)
the trait of being intensely emotional	feelings of great warmth and intensity
any object of warm affection or devotion
a strong feeling or emotion
a feeling of strong sexual desire
an irrational but irresistible motive for a belief or action
something that is desired intensely