Ruse to use when short of space (4)
I believe the answer is:
ploy
'ruse' is the definition.
(both can mean a trick or scheme)
'use when short of space' is the wordplay.
I cannot quite understand how this works, but
'of' could be 'o' and 'o' is located in the answer.
'use' could be 'ply' (plying is a kind of using) and 'ply' is found in the remaining letters.
No letters remain.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for ploy that I've seen before include "Ruse, stratagem" , "Tactical scheme" , "Game manoeuvre" , "Device" , "Cunning manoeuvre to gain advantage" .)