\begin{definition}[Definition:Cylinder/Axis]
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{{EuclidSaid}}
:''{{Definition:Euclid's Definitions - Book XI/22 - Axis of Cylinder}}''
{{EuclidDefRefNocat|XI|22|Axis of Cylinder}}
In the above diagram, the '''axis''' of the cylinder $ACBEFD$ is the straight line $GH$.
\end{definition}