\begin{definition}[Definition:Euclid's Definitions - Book I/18 - Semicircle]
{{EuclidSaid}}
:'' A '''semicircle''' is the figure contained by the diameter and the circumference cut off by it. And the center of the semicircle is the same as that of the circle.''
{{EuclidDefRef|I|18|Semicircle}}
\end{definition}