The bard reinvented dimension (7)
I believe the answer is:
breadth
'dimension' is the definition.
(breadth is a kind of dimension)
'the bard reinvented' is the wordplay.
'reinvented' indicates an anagram.
'the'+'bard'='thebard'
'thebard' with letters rearranged gives 'BREADTH'.
(Other definitions for breadth that I've seen before include "Wideness" , "Wide range" , "Latitude, broadness" , "Red bath (anag)" , "Extent from side to side" .)