Trefoil leaf in paste? (8)

I believe the answer is:

shamrock

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'trefoil' is the definition.
(shamrock is a kind of trefoil)

I cannot understand how the rest of the clue works.

(Other definitions for shamrock that I've seen before include "Clover-like plant" , "symbolic of Ireland" , "Pressed grape-juice" , "Clover native to Ireland" , "The national Irish trefoil" .)

I've seen this clue in The Times.

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