Definition of blot one's copybook in English:

blot one's copybook

  • British Tarnish one’s good reputation: she saw her sister blot her copybook by being quoted in the press
    More example sentences
    • There are only two minor plateaus blotting her copybook - one in early February and one in mid-April.
    • Nobody expects him to get a big government rail job - he blotted his copybook with civil servants over English Heritage - though his experience would make him an obvious choice.
    • Another has blotted his copybook on his two most recent starts after a promising start to his chasing career.
See parent entry: blot

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