Post, column (6)
I believe the answer is:
pillar
This clue is a double definition.
'post' is the first definition.
(a pillar is a post or column)
'column' is the second definition.
(both can mean an upright structure)
(Other definitions for pillar that I've seen before include "Upright column" , "Column, support" , "Supporting column" , "Tall vertical structure, of stone say" , "Supporter" .)