Column bloke is rewriting (7)
I believe the answer is:
obelisk
'column' is the definition.
(obelisk is a kind of column)
'bloke is rewriting' is the wordplay.
'rewriting' indicates anagramming the letters.
'bloke'+'is'='blokeis'
'blokeis' anagrammed gives 'OBELISK'.
(Other definitions for obelisk that I've seen before include "Kind of monument, tall sloping pillar" , "Monument with tall pillar and tapering top" , "Square stone column that tapers" , "Tapering monumental pillar" , "Ancient Egyptian monument" .)