Tease, as top head is missing (4)

I believe the answer is:

mock

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'tease' is the definition.
(I know that tease is a more specific form of the action mock)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for mock that I've seen before include "Unreal; ridicule" , "Treat with contempt -- imitation" , "Deride - false" , "Tease or laugh at" , "Scoff at" .)

I've seen this clue in The Daily Express.

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