Is there a word for one side in a pair?

Is there a word for one side in a pair? In a conversation it would the the interlocutor, but I'm looking for a generic term.

Solution 1:

The English word for "one of a pair" is in fact "pair". You can ask: "Where is the pair to this shoe?" "Pair" has two meanings.

Solution 2:

I'm going with "counterpart", as suggested to me off-site. Thanks for the feedback though!

Solution 3:

This is one of those occasions when one realizes the unique abilities of each language. English with most number of words among the world languages, does not have a word for each member of a pair. We, hence, use the word "pair" (as in "where is the other pair?") when we mean a member of the pair. In Persian we do not have this problem as there is a word for members of the dyad. The pair or couple is "Joft" (جفت) and each member of that pair is a "lengeh" (لنگه.) Persian also have a word for a mismatched pair: "lengeh be lengeh!"

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Solution 4:

Until we find a more complicated esoteric word that matches your requirements, try "complement" for a while.