Supporting column (9)
(Other definitions for stanchion that I've seen before include "Upright" , "Post or rod used as a support" , "Vertical post or rod as a support" .)
'supporting column' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pillar that I've seen before include "Building support" , "Vertical stone support" , "person providing reliable support" , "Upright column" , "Stylite would live on it" .)