Want to desert (6)
I believe the answer is:
defect
I believe this clue is a double definition.
'want' is the first definition.
(I've seen this before)
'desert' is the second definition.
(I know that desert can be written as defect)
'to' is the link.
(Other definitions for defect that I've seen before include "Go over to the enemy - it's a flaw" , "Abandon one's country in favour of an opposing one" , "mistake" , "'Flaw, imperfection (6)'" , "Lack" .)