open vs start

open and start both are nouns.

Word	Noun	Adjective	Verb	Adverb
open	Yes	Yes	Yes	No
start	Yes	No	Yes	No

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

Other hypernyms of open include commence, embark on, start up.

open (noun)	start (noun)
information that has become public	the act of starting something
a tournament in which both professionals and amateurs may play	a sudden involuntary movement
a clear or unobstructed space or expanse of land or water	a turn to be a starter (in a game at the beginning)
where the air is unconfined	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

open (adjective)	start (adjective)
ready or willing to receive favorably
affording unobstructed entrance and exit; not shut or closed
affording free passage or access
(set theory) of an interval that contains neither of its endpoints
open and observable; not secret or hidden
used of mouth or eyes
ready for business
not having been filled
(of textures) full of small openings or gaps
openly straightforward and direct without reserve or secretiveness
not requiring union membership
open to or in view of all
possibly accepting or permitting
without undue constriction as from e.g. tenseness or inhibition
having no protecting cover or enclosure
affording free passage or view
with no protection or shield
accessible to all
not sealed or having been unsealed
not brought to a conclusion; subject to further thought
not defended or capable of being defended

open (verb)	start (verb)
make available	take the first step or steps in carrying out an action
become available	set in motion, cause to start
make the opening move	play in the starting lineup
cause to open or to become open	bring into being
become open	get off the ground
spread out or open from a closed or folded state	begin or set in motion
display the contents of a file or start an application as on a computer	get going or set in motion
afford access to	depart for someplace
start to operate or function or cause to start operating or functioning	bulge outward
begin or set in action, of meetings, speeches, recitals, etc.	move or jump suddenly, as if in surprise or alarm
have an opening or passage or outlet	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