constancy vs faithfulness

constancy and faithfulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
constancy	Yes	No	No	No
faithfulness	Yes	No	No	No

As nouns, faithfulness is a hypernym of constancy; that is, faithfulness is a word with a broader meaning than constancy:

constancy: faithfulness and dependability in personal attachments (especially sexual fidelity)
faithfulness: the quality of being faithful

Other hypernyms of constancy include fidelity.

constancy (noun)	faithfulness (noun)
the quality of being enduring and free from change or variation	the quality of being faithful
faithfulness and dependability in personal attachments (especially sexual fidelity)
(psychology) the tendency for perceived objects to give rise to very similar perceptual experiences in spite of wide variations in the conditions of observation