no-brainer vs undertaking

no-brainer and undertaking both are nouns.

Word	Noun	Adjective	Verb	Adverb
no-brainer	Yes	No	No	No
undertaking	Yes	No	No	No

As nouns, undertaking is a hypernym of no-brainer; that is, undertaking is a word with a broader meaning than no-brainer:

Other hypernyms of no-brainer include labor, labour, project, task.

no-brainer (noun)	undertaking (noun)
anything that requires little thought	any piece of work that is undertaken or attempted
	the trade of a funeral director