Definition of knock (or hit) someone for six in English:

knock (or hit) someone for six

phrase

British
informal
  • Utterly surprise or overcome someone.

    ‘this business has knocked her for six’
    • ‘I take each day as it comes but it knocks you for six.’
    • ‘I'm not a publicity minded guy, so it's really knocked me for six.’
    • ‘To be told by someone you had only just met that it wouldn't work knocked me for six.’
    • ‘My mother's death, in June 2000, really knocked him for six.’
    • ‘My marriage had gone through a bad time and that knocked me for six.’
    • ‘She is one in a million, such a lively and positive person, and this knocked her for six.’
    • ‘The sexual innuendo is so utterly out of left field that it knocks you for six.’
    • ‘The clocks changing has knocked me for six - I'm perky as anything in the morning, but come afternoon I feel like I've been hit by a brick wall.’
    • ‘When you are just starting out in life you have got it all to do and it just knocked her for six.’
    • ‘I am very angry if they put a ban on my business, it will knock me for six.’
    amaze, astonish, dumbfound, stagger, surprise, startle, stun, stupefy, daze, nonplus
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