Collection is a related term of pair.
In obsolete|lang=en terms the difference between collection and pair
is that
collection is (obsolete) the act of inferring or concluding from premises or observed facts; also, that which is inferred while
pair is (obsolete) to impair.
As nouns the difference between collection and pair
is that
collection is a set of items or amount of material procured or gathered together while
pair is two similar or identical things taken together; often followed by of.
As a verb pair is
to group into sets of two or
pair can be (obsolete) to impair.