commonplace vs humdrum

commonplace and humdrum both are nouns.

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

As adjectives, commonplace and humdrum are synonyms defined as:

Other synonyms of commonplace include prosaic, unglamorous, unglamourous.

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

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