monotony vs constancy

monotony and constancy both are nouns.

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

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

Other hypernyms of monotony include stability.

monotony (noun)	constancy (noun)
the quality of wearisome constancy, routine, and lack of variety	the quality of being enduring and free from change or variation
constancy of tone or pitch or inflection	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