Naps standing up on bridge (4)
I believe the answer is:
span
'bridge' is the definition.
(synonyms)
'naps standing up' is the wordplay.
'standing up' is a reversal indicator (in a down clue up is reverse order).
'naps' written backwards gives 'SPAN'.
'on' is the link.
(Other definitions for span that I've seen before include "Bridge - rotated" , "Bridge or range" , "Extent - 9 inches" , "period of time" , "Extent of bridge or life" .)