Bridge distance (4)
I believe the answer is:
span
'bridge distance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for span that I've seen before include "Go across" , "Extent - 23cm" , "Length of bridge - 9 inches!" , "Extent, space for odd pans" , "Full extent end to end" .)