sameness vs humdrum

sameness and humdrum both are nouns.

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

As nouns, sameness and humdrum are synonyms defined as:

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

Other synonyms of sameness include monotony.

sameness (noun)	humdrum (noun)
the quality of being alike	the quality of wearisome constancy, routine, and lack of variety
the quality of wearisome constancy, routine, and lack of variety

sameness (adjective)	humdrum (adjective)
	tediously repetitious or lacking in variety
	not challenging; dull and lacking excitement