first step vs commencement

first step and commencement both are nouns.

Word	Noun	Adjective	Verb	Adverb
first step	Yes	No	No	No
commencement	Yes	No	No	No

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

Other hypernyms of first step include beginning, start.

first step (noun)	commencement (noun)
the first of a series of actions	the act of starting something
	an academic exercise in which diplomas are conferred
	the time at which something is supposed to begin