showtime vs commencement

showtime and commencement both are nouns.

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

As nouns, showtime and commencement are synonyms defined as:

showtime and commencement: the time at which something is supposed to begin

Other synonyms of showtime include beginning, first, get-go, kickoff, offset, outset, start, starting time.

showtime (noun)	commencement (noun)
the time at which something is supposed to begin	the act of starting something
	an academic exercise in which diplomas are conferred
	the time at which something is supposed to begin