humdrum vs commonplace

humdrum and commonplace both are nouns.

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

As adjectives, humdrum and commonplace are synonyms defined as:

Other synonyms of humdrum include prosaic, unglamorous, unglamourous.

humdrum (noun)	commonplace (noun)
the quality of wearisome constancy, routine, and lack of variety	a trite or obvious remark

humdrum (adjective)	commonplace (adjective)
tediously repetitious or lacking in variety	not challenging; dull and lacking excitement
not challenging; dull and lacking excitement	repeated too often; overfamiliar through overuse
	completely ordinary and unremarkable