\begin{definition}[Definition:Euclid's Definitions - Book X (II)/1 - First Binomial]
{{EuclidSaid}}
:''Given a rational straight line and a binomial, divided into its terms, such that the square on the greater term is greater than the square on the lesser by the square on a straight line commensurable in length with the greater, then, if the greater term be commensurable in length with the rational straight line set out, let the whole be called a '''first binomial''' straight line;''
{{EuclidDefRef|X (II)|1|First Binomial}}
\end{definition}