get going vs start

get going is not a noun while start is a noun.

Word	Noun	Adjective	Verb	Adverb
get going	No	No	Yes	No
start	Yes	No	Yes	No

As verbs, start is a hypernym of get going; that is, start is a word with a broader meaning than get going:

Other hypernyms of get going include begin, commence, get, get down, set about, set out, start out.

As verbs, get going and start are synonyms defined as:

Other synonyms of get going include go.

get going (noun)	start (noun)
	the act of starting something
	a sudden involuntary movement
	a turn to be a starter (in a game at the beginning)
	the advantage gained by beginning early (as in a race)
	a signal to begin (as in a race)
	the beginning of anything
	a line indicating the location of the start of a race or a game
	the time at which something is supposed to begin

get going (verb)	start (verb)
start to be active	take the first step or steps in carrying out an action
begin or set in motion	set in motion, cause to start
	play in the starting lineup
	bring into being
	get off the ground
	begin or set in motion
	get going or set in motion
	depart for someplace
	bulge outward
	move or jump suddenly, as if in surprise or alarm
	begin work or acting in a certain capacity, office or job
	begin an event that is implied and limited by the nature or inherent function of the direct object
	have a beginning, in a temporal, spatial, or evaluative sense
	have a beginning characterized in some specified way