\begin{definition}[Definition:Euclid's Definitions - Book XI/3 - Line at Right Angles to Plane]
{{EuclidSaid}}
:''A '''straight line''' is '''at right angles to a plane''' when it makes right angles with all the straight lines which meet it and are in the plane.''
{{EuclidDefRef|XI|3|Line at Right Angles to Plane}}
\end{definition}