Insincere talk Immanuel heard (4)
I believe the answer is:
cant
'insincere talk' is the definition.
(I've seen this before)
'immanuel heard' is the wordplay.
'immanuel' becomes 'kant' (I've seen this in another clue).
'heard' shows a homophone (sound like).
'kant' is a homophone of 'CANT'.
(Other definitions for cant that I've seen before include "Hypocritical speech" , "Special jargon of a group" , "Insincere talk, pious platitudes" , "Hypocritical talk; slope" , "Slope; thieves' talk" .)