icebreaker vs commencement

icebreaker and commencement both are nouns.

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

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

Other hypernyms of icebreaker include beginning, start.

icebreaker (noun)	commencement (noun)
a beginning that relaxes a tense or formal atmosphere	the act of starting something
a ship with a reinforced bow to break up ice and keep channels open for navigation	an academic exercise in which diplomas are conferred
	the time at which something is supposed to begin