risky venture vs undertaking

risky venture and undertaking both are nouns.

Word	Noun	Adjective	Verb	Adverb
risky venture	Yes	No	No	No
undertaking	Yes	No	No	No

As nouns, undertaking is a hypernym of risky venture; that is, undertaking is a word with a broader meaning than risky venture:

Other hypernyms of risky venture include labor, labour, project, task.

risky venture (noun)	undertaking (noun)
a wild and exciting undertaking (not necessarily lawful)	any piece of work that is undertaken or attempted
	the trade of a funeral director