Drop last trace of fat to be highly desirable (4)
I believe the answer is:
plum
'be highly desirable' is the definition.
(plum can mean excellent)
'drop last trace of fat' is the wordplay.
'last' indicates one should take the final letters.
'trace of fat' becomes 'lum' (I can't justify this - if you can you should give a lot more credence to this answer).
The last letter of 'drop' is 'p'.
'p'+'lum'='PLUM'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for plum that I've seen before include "excellent?" , "murderer" , "Fruit; something choice" , "Oval fruit with single hard stone" , "Shade" .)