monotony vs sameness

monotony and sameness both are nouns.

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

As nouns, monotony and sameness are synonyms defined as:

monotony and sameness: the quality of wearisome constancy, routine, and lack of variety

Other synonyms of monotony include humdrum.

monotony (noun)	sameness (noun)
the quality of wearisome constancy, routine, and lack of variety	the quality of being alike
constancy of tone or pitch or inflection	the quality of wearisome constancy, routine, and lack of variety