In lang=en terms the difference between merge and pair
is that
merge is to combine into a whole while
pair is to suit; to fit, as a counterpart.
As verbs the difference between merge and pair
is that
merge is to combine into a whole while
pair is to group into sets of two or
pair can be (obsolete) to impair.
As nouns the difference between merge and pair
is that
merge is a joining together of two flows while
pair is two similar or identical things taken together; often followed by of.