Female dog losing head in desire (4)
I believe the answer is:
itch
'desire' is the definition.
(itch is a kind of desire)
'female dog losing head' is the wordplay.
'female dog' becomes 'bitch' (I've seen this before).
'losing head' means to remove the first letter.
'bitch' with its first letter removed is 'ITCH'.
'in' acts as a link.
(Other definitions for itch that I've seen before include "cause irritation" , "It needs to be scratched" , "following seven years in union?" , "Seven-yearly desire" , "Restless longing" .)