prosaic vs humdrum

prosaic is not a noun while humdrum is a noun.

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

As adjectives, prosaic and humdrum are synonyms defined as:

Other synonyms of prosaic include commonplace, unglamorous, unglamourous.

prosaic (noun)	humdrum (noun)
	the quality of wearisome constancy, routine, and lack of variety

prosaic (adjective)	humdrum (adjective)
not challenging; dull and lacking excitement	tediously repetitious or lacking in variety
lacking wit or imagination	not challenging; dull and lacking excitement
not fanciful or imaginative