Distance across (7)
(Other definitions for breadth that I've seen before include "generosity of mind" , "Extent from side to side" , "Red bath (anag)" , "Wide measurement" , "Wide range" .)
'distance across' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for span that I've seen before include "Extent - 23cm" , "A bridge or measure of width" , "Extent from end to end or across" , "Width of wings" , "Extend from end to end, say bridge" .)