Rigidly upright (5)
I believe the answer is:
erect
'rigidly upright' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for erect that I've seen before include "Upright; construct" , "Rigidly upright" , "Construct - perpendicular" , "Found" , "Upright; put up" .)