Select the geometry you want to rotate.
From Toolbar
Click More Tools → Edit → Basepoint rotate
From Command Line
Tap the spacebar:
Click Base Point Rotate
Specify starting Node (base point)
Use S hotkey to snap to a corner or midpoint.
Draw in any direction to specify where the rotation angle will calculate from.
Rotate the object.
The object rotates around that basepoint, rather than around the centroid of the object.
<aside>