Achilles’ heel - definition and synonyms

noun [singular] 

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/əˌkɪliːz ˈhiːl/
  1. a weak feature of someone or something that is otherwise strong, which makes them open to attack or failure

    Michigan's defense has been their Achilles heel this entire season.

    Government debt is the Achilles' heel of their economy.

     Synonyms and related words