grin like a Cheshire cat

Attested since at least the 1780s. The reason why Cheshire was combined with cat is disputed: see here for more information.

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grin like a Cheshire cat (third-person singular simple present grins like a Cheshire cat, present participle grinning like a Cheshire cat, simple past and past participle grinned like a Cheshire cat)

1. (simile) To smile broadly, especially in a self-satisfied way.

   Synonym: smile from ear to ear

   John ended the set with a beautiful serve, an ace, and could not help grinning like a Cheshire cat.

   • 1788, Francis Grose, A classical dictionary of the vulgar tongue, 2nd corrected and enlarged edition, London:

     CHESHIRE CAT. He grins like a Cheshire cat; said of any one who shows his teeth and gums in laughing.

   • 1792, John Wolcot (under the pseudonym Peter Pindar), Pair of Lyric Epistles:

     Lo, like a Cheshire cat our court will grin.

   • 1967, Barbara Sleigh, Jessamy, Sevenoaks, Kent: Bloomsbury, published 1993, →ISBN, page 127:

     ‘It’s almost as if we’ve gone silly with happiness,’ said Marcus two days later. ‘Everyone in the house going round grinning like a lot of Cheshire Cats! The family I mean.’ ‘And Jess,’ said Kitto quickly. ‘Oh well, Jess is as good as family,’ said Fanny comfortably. Jessamy said nothing, but she looked up quickly and her smile would have rivalled any Cheshire Cat.