ET from the planet Melmac (3)
I believe the answer is:
alf
'et from the planet melmac' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alf that I've seen before include "Great king briefly" , "Sir - Ramsey, England footballer and manager" , "-- Garnett, bigoted TV?character" , "Mr Garnett" , "Chap" .)