Say nothing? Am false! (4)

I believe the answer is:

sham

'false' is the definition.
(I've seen this before)

'say nothing? am' is the wordplay.
'say nothing?' becomes 'sh' ('sh' is said to tell someone to say nothing).
'sh'+'am'='SHAM'

(Other definitions for sham that I've seen before include "Bogus hams" , "Pretense; bogus" , "Phoney sort of hams" , "Feign" , "Phoney kind of hams" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app