start vs set off

start is a noun but set off is not a noun.

Word	Noun	Adjective	Verb	Adverb
start	Yes	No	Yes	No
set off	No	No	Yes	No

As verbs, set off is a hyponym of start; that is, set off is a word with a more specific, narrower meaning than start:

As verbs, start and set off are synonyms defined as:

Other synonyms of start include depart, part, set forth, set out, start out, take off.

start (noun)	set off (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

start (verb)	set off (verb)
take the first step or steps in carrying out an action	cause to burst with a violent release of energy
set in motion, cause to start	set in motion or cause to begin
play in the starting lineup	direct attention to, as if by means of contrast
bring into being	provoke or stir up
get off the ground	put in motion or move to act
begin or set in motion	depart for someplace
get going or set in motion	make up for
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