Lifetime of bridge? (4)
I believe the answer is:
span
I believe this is a double definition.
'lifetime' is the first definition.
(I've seen this in another clue)
'bridge?' is the second definition.
(I know that bridge can be written as span)
'of' is the link.
(Other definitions for span that I've seen before include "Extent of 20" , "Distance or interval between two points" , "Duration, length" , "Distance between two points in time or place" , "The total spread" .)