large order vs undertaking

large order and undertaking both are nouns.

Word	Noun	Adjective	Verb	Adverb
large order	Yes	No	No	No
undertaking	Yes	No	No	No

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

Other hypernyms of large order include labor, labour, project, task.

large order (noun)	undertaking (noun)
a formidable task or requirement	any piece of work that is undertaken or attempted
	the trade of a funeral director