How to keep a secret? Not at all! (4,7,2)
I believe the answer is:
dont mention it
'not at all' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for dont mention it that I've seen before include "It was nothing" , "That's all right" , "Refrain from talking about the situation" , "Let's not discuss computers" , "keep it secret" .)