Secretly thinks grim pastor lays it on a bit thick (7)

I believe the answer is:

impasto

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'lays it on a bit thick' is the definition.
I can't tell whether this defines the answer.

'secretly thinks grim pastor' is the wordplay.
'secretly' indicates a hidden word.
'IMPASTO' is hidden within 'thinks grim pastor'.

Can you help me to learn more?

(Other definitions for impasto that I've seen before include "Thickly-applied painting technique" , "Thickly-applied paint" , "Art technique of laying paint on thickly" , "artistic technique" , "Painting with pigment laid on thick" .)

I've seen this clue in The Irish Times.

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