introduction vs first appearance

introduction and first appearance both are nouns.

Word	Noun	Adjective	Verb	Adverb
introduction	Yes	No	No	No
first appearance	Yes	No	No	No

As nouns, introduction and first appearance are synonyms defined as:

Other synonyms of introduction include debut, entry, launching, unveiling.

introduction (noun)	first appearance (noun)
the act of putting one thing into another	the act of beginning something new
the act of beginning something new
the act of starting something for the first time; introducing something new
the first section of a communication
formally making a person known to another or to the public
a basic or elementary instructional text
a new proposal