# Definition:Relation/Unary Relation

## Definition

As a special case of an $n$-ary relation on $S$, note that when $n = 1$ we define a unary relation on $S$ as:

$\mathcal R \subseteq S$

That is, a unary relation is a subset of $S$.

## Linguistic Note

The word unary is pronounced yoo-nary.

Hence when the indefinite article precedes it, the form is (for example) a unary operation.