Con the Greek’s cross, knocking block off damsel? (6)

I believe the answer is:

chisel

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'con' is the definition.
(I know that con can be written as chisel)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for chisel that I've seen before include "Hand tool to shape wood" , "Hammered cutting tool" , "Tool for shaping wood or metal" , "Sharp-edged metal tool" , "Tool with bevelled edge for shaping wood" .)

I've seen this clue in the Sydney Morning Herald.

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