PAIR

Two similar or identical things taken together; often followed by of.

"I couldn't decide which of the pair of designer shirts I preferred, so I bought the pair."

Two people in a relationship, partnership or friendship.

"Spouses should make a great pair."

Used with binary nouns (often in the plural to indicate multiple instances, since such nouns are plural only, except in some technical contexts)

"a pair of scissors; two pairs of spectacles; several pairs of jeans"

To group into one or more sets of two.

"The wedding guests were paired boy/girl and groom's party/bride's party."

To bring two (animals, notably dogs) together for mating.

To engage (oneself) with another of opposite opinions not to vote on a particular question or class of questions.

To impair, to make worse.

To become worse, to deteriorate.