Send a watch up (5)
I believe the answer is:
remit
'send' is the definition.
(I've seen this before)
'a watch up' is the wordplay.
'a watch' becomes 'timer' (a watch might be used to time something).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'timer' backwards is 'REMIT'.
(Other definitions for remit that I've seen before include "Scope - send money" , "Assigned task or area" , "Brief - transfer" , "forward" , "The - Papers (M. Amis)" .)