Noun

(en noun)

An opponent or enemy.

* Milton

antagonist of Heaven's Almighty King

* Hooker

our antagonists in these controversies

One who antagonizes or stirs.

(biochemistry) A chemical that binds to a receptor but does not produce a physiological response, blocking the action of agonist chemicals.

* 2001': The calcium '''antagonists represent one of the top ten classes of prescription drugs in terms of commercial value, with worldwide sales of nearly $10 billion in 1999. — Leslie Iversen, ''Drugs: A Very Short Introduction (Oxford 2001, p. 41)

The main character or force opposing the protagonist in a literary work or drama.

(anatomy) A muscle that acts in opposition to another.

A flexor, which bends a part, is the antagonist of an extensor, which extends it.

Noun

(en noun)

Either of two parts that fit together, or complement one another.

''Those brass knobs and their hollow counterparts interlock perfectly

* {{quote-news, year=2012, date=November 7, author=Matt Bai, title=Winning a Second Term, Obama Will Confront Familiar Headwinds, work=New York Times citation

, passage=Mr. Obama never found a generational counterpart among conservatives in Congress like Paul D. Ryan or Eric Cantor; instead, there was a mutual animosity.}}

(legal) A duplicate of a legal document.

One which resembles another

One which has corresponding functions or characteristics.

* {{quote-news

, year=2011 , date=November 12 , author= , title=International friendly: England 1-0 Spain , work=BBC Sport citation , page= , passage=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.}}