Is she speechless? (3)
I believe the answer is:
mum
'speechless?' is the definition.
(I've seen this in another clue)
I cannot 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 "Informal palindromic mother" , "Keep quiet, mother" , "Tight-lipped" , "member of the family" , "Parent - shtoom" .)