know like the back of one's hand

• know like the palm of one's hand

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know like the back of one's hand (third-person singular simple present knows like the back of one's hand, present participle knowing like the back of one's hand, simple past knew like the back of one's hand, past participle known like the back of one's hand)

1. (transitive, simile) To be intimately knowledgeable about something.

   He knows the software like the back of his hand, and can often solve problems over the phone, without looking.

   • 1938, Norman Lindsay, Age of Consent, 1st Australian edition, Sydney, N.S.W.: Ure Smith, published 1962, →OCLC, page 218:

     "I can; know that country like the back of my hand. You haven't got a road map, I suppose. Well, no matter, I'll give you the lay of the land without it."

   • 2024 April 27, Tim Bano, quoting Sanaz Toossi, “It's a play born of rage”, in FT Weekend, Life & Arts, page 15:

     “I know American audiences like the back of my hand,” she says, sitting in a dressing room in London at the end of a long day of rehearsals; […]

• know inside and out
• know like a book

• give someone the back of one's hand