commutant

Century Dictionary and Cyclopedia

1. n. In algebra, an oblong block of figures, denoting the sum of a number of products, each consisting of as many factors as the block has rows, and each factor being formed by compounding as umbræ the constituents in one row, the different terms being due to permutation with change of sign, in every possible way, of the constituents of every column after the first.

Wiktionary

1. n. algebra, logic The subset of all elements of a semigroup that commute with the elements of a given subset