The Irish mathematical physicist, John Lighton Synge, created the two-person zero-sum game (see Game theory) of Circ to emphasize the circular reasoning which is implicit in the defining process of any standard dictionary. John Lighton Synge (born 23 March 1897 in Dublin, Ireland and died 30 March 1995 in Dublin, Ireland) was an Irish physicist. ... Game theory is a branch of applied mathematics that uses models to study interactions with formalised incentive structures (games). It has applications in a variety of fields, including economics, international relations, evolutionary biology, political science, and military strategy. ... Manual of Specialised Lexicography, Henning Bergenholtz/Sven Tarp (eds. ...

Procedure:

1. Each of the two players is given a copy of the same standard dictionary;
2. the referee gives each a slip of paper with the same word (found in this dictionary) written on each slip -- word chosen so that it has synonyms in its definition, but (preferably) the definition of any synonym does not (in that dictionary) list a synonym which is the originally assigned word;
3. at "Go!", each looks up the assigned word, finds a synonym, looks that up, finds a synonym, etc;
4. the first player to be led, by this synonymous process, back to the originally assigned word cries "Circ!" and wins the game (unless his opponent successfully challenges the procedure of the alleged winner).

Teachers have found this a popular procedure for teaching English or some other language.