\begin{definition}[Definition:Euclid's Definitions - Book X/2 - Commensurable in Square]
{{EuclidSaid}}
:''Straight lines are '''commensurable in square''' when the squares on them are measured by the same area, and '''incommensurable in square''' when the squares on them cannot possibly have any area as a common measure.''
{{EuclidDefRef|X|2|Commensurable in Square}}
\end{definition}