Bitterness of topped golf stroke (4)

I believe the answer is:

edge

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'bitterness' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for edge that I've seen before include "Rim or sharp side of knife" , "Boundary; advantage" , "Border - meeting place" , "Side, brink" , "Border; intense quality" .)

I've seen this clue in The Telegraph.

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