intromission vs insertion

intromission and insertion both are nouns.

Word	Noun	Adjective	Verb	Adverb
intromission	Yes	No	No	No
insertion	Yes	No	No	No

As nouns, intromission and insertion are synonyms defined as:

Other synonyms of intromission include introduction.

intromission (noun)	insertion (noun)
the act of putting one thing into another	the act of putting one thing into another
	a message (spoken or written) that is introduced or inserted