To complete the analogy, the opposite of IRRITATE is Soothe.
In this analogy, the word "INITIATE" is the opposite of "CONCLUDE." Therefore, to find the word that is the opposite of "IRRITATE," we need to think of a word that means the opposite of irritating. One possible word that fits this description is "Soothe." So the completed analogy is:
INITIATE is to CONCLUDE as IRRITATE is to Soothe.
The probable question may be:
"INITIATE is to CONCLUDE as IRRITATE is to"