opening vs introductory

opening is a noun but introductory is not a noun.

Word	Noun	Adjective	Verb	Adverb
opening	Yes	Yes	No	No
introductory	No	Yes	No	No

opening (noun)	introductory (noun)
a recognized sequence of moves at the beginning of a game of chess
the act of opening something
becoming open or being made open
the first of a series of actions
a vacant or unobstructed space that is man-made
an entrance equipped with a hatch; especially a passageway between decks of a ship
an aperture or hole that opens into a bodily cavity
a possible alternative
the initial part of the introduction
the first performance (as of a theatrical production)
a ceremony accompanying the start of some enterprise
an open or empty space in or between things
opportunity especially for employment or promotion

opening (adjective)	introductory (adjective)
first or beginning	serving as a base or starting point
	serving to open or begin
	serving as an introduction or preface