Silent disease - no additional comment (3)
I believe the answer is:
mum
'silent' is the definition.
(keep mum)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mum that I've seen before include "Quiet; relative" , "old lady" , "Keep it secret from mother?" , "Silent; parent" , "Tight-lipped" .)