Doctor with huge son? Rubbish (5)
I believe the answer is:
dross
'rubbish' is the definition.
(I've seen this in another clue)
'doctor with huge son?' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'with' is a charade indicator (letters next to each other).
'huge' becomes 'os' (abbreviation for outsize).
'son?' becomes 's' (genealogical abbreviation for son).
'dr'+'os'+'s'='DROSS'
(Other definitions for dross that I've seen before include "Waste from molten metal" , "Rubbish; impurities" , "Anything worthless" , "Refuse - dregs" , "It's Poor" .)