Silence a so-called lady singer (4)
I believe the answer is:
gaga
'lady singer' is the definition.
(Lady Gaga the singer)
'silence a' is the wordplay.
'silence' becomes 'gag' (gagging is a kind of silencing).
'gag'+'a'='GAGA'
'so-called' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for gaga that I've seen before include "crackers" , "Very fond of" , "Lady < > in a senile" , "Senile - slightly crazy" , "Bats" .)