counterpart

Etymology

Recorded since 1451, originally as countre part "duplicate of a legal document", from Old French contrepartie, itself from contre (“facing, opposite”) (from Latin contra (“against”)) + partie (“copy of a person or thing”) (originally past participle of partīre (“to divide”)). Equivalent to counter- + part.

noun

1. Either of two parts that fit together, or complement one another.
   Those brass knobs and their hollow counterparts interlock perfectly.
   Mr. Obama never found a generational counterpart among conservatives in Congress like Paul D. Ryan or Eric Cantor; instead, there was a mutual animosity. November 7, 2012, Matt Bai, “Winning a Second Term, Obama Will Confront Familiar Headwinds”, in New York Times
2. (law) A duplicate of a legal document.
3. One who or that which resembles another.
4. One who or that which has corresponding functions or characteristics.
   Its incompleteness in this respect makes the timetable of less value than some of its Continental counterparts, such as the French Horaires Mayeux; nevertheless, it is fair value at 5s. 1962 July, “Talking of Trains: The new all-line timetable”, in Modern Railways, page 10
   England's attacking impetus was limited to one shot from Lampard that was comfortably collected by keeper Iker Casillas, but for all Spain's domination of the ball his England counterpart Joe Hart was unemployed. November 12, 2011, “International friendly: England 1-0 Spain”, in BBC Sport
5. (paleontology) Either half of a flattened fossil when the rock has split along the plane of the fossil.

verb

1. (transitive) To counterbalance.