groundbreaking vs commencement

groundbreaking and commencement both are nouns.

Word	Noun	Adjective	Verb	Adverb
groundbreaking	Yes	Yes	No	No
commencement	Yes	No	No	No

As nouns, commencement is a hypernym of groundbreaking; that is, commencement is a word with a broader meaning than groundbreaking:

groundbreaking: the ceremonial breaking of the ground to formally begin a construction project
commencement: the act of starting something

Other hypernyms of groundbreaking include beginning, start, ceremony.

groundbreaking (noun)	commencement (noun)
the ceremonial breaking of the ground to formally begin a construction project	the act of starting something
	an academic exercise in which diplomas are conferred
	the time at which something is supposed to begin

groundbreaking (adjective)	commencement (adjective)
being or producing something like nothing done or experienced or created before