embark on vs start

embark on is not a noun while start is a noun.

Word	Noun	Adjective	Verb	Adverb
embark on	No	No	Yes	No
start	Yes	No	Yes	No

As verbs, embark on and start are synonyms defined as:

Other synonyms of embark on include commence, start up.

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

Other hypernyms of embark on include begin, commence, lead off.

embark on (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

embark on (verb)	start (verb)
get off the ground	take the first step or steps in carrying out an action
	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