level best

From level (“well balanced; even, steady”) +‎ best.

• (Received Pronunciation) IPA^(key): /ˌlɛvl̩ ˈbɛst/
• (Received Pronunciation) IPA^(key): /ˌlɛv(ə)l ˈbɛst/

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• Rhymes: -ɛst
• Hyphenation: lev‧el best

level best (plural level bests)

1. (idiomatic) The very best that one can do.
   • 1885 September, H[enry] Rider Haggard, “Solomon’s Road”, in King Solomon’s Mines, London, Paris: Cassell & Company, […], published 1887, →OCLC, page 102:

     Then came a pause, each man aiming his level best, as indeed one is likely to do when one knows that life itself depends upon the shot.

   • 1920, John Galsworthy, “Dartie versus Dartie”, in In Chancery, London: William Heinemann, →OCLC, part II, page 186:

     Val walked out behind his mother, chin squared, eyelids drooped, doing his level best to despise everybody.

   • 1922 February, James Joyce, “[Episode 13: Nausicaa]”, in Ulysses, Paris: Shakespeare and Company, […], →OCLC, part II [Odyssey], page 341:

     ―Say papa, baby. Say pa pa pa pa pa pa pa. / And baby did his level best to say it for he was very intelligent for eleven months everyone said and big for his age and the picture of health, a perfect little bunch of love, and he would certainly turn out to be something great, they said.

   • 2022 October 16, Jenna Scherer, “An Enticing House of the Dragon Crowns Westeros’ New Ruler”, in The A.V. Club‎, archived from the original on 2022-10-28:

     The king-to-be is sulking in a carriage beside his mother, who’s doing her level best to prepare her son for what’s to come.

• personal best

• “one’s level best” under “level, adj. and adv.”, in OED Online ⁠, Oxford, Oxfordshire: Oxford University Press, March 2023.
• “level best, phrase” under “level, adj.”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.