indefatigable

From Middle French, from Latin indēfatīgābilis (“untiring”), from in- (“not”) + dēfatīgō (“to tire out”).

• (Received Pronunciation) IPA^(key): /ˌɪn.dɪˈfæt.ɪ.ɡə.bəl/
• (General American, General Australian) IPA^(key): /ˌɪn.dəˈfæt.ɪ.ɡə.bəl/, [ˌɪn.dəˈfæɾ.ɪ.ɡə.bəl]

  • Audio (General Australian):

    (file)

• (sometimes proscribed) IPA^(key): /ˌɪn.dɪ.fəˈti.ɡə.bəl/, /ˌɪn.də-/

  • Audio (Northern California):

    (file)

• Hyphenation: in‧de‧fa‧tig‧a‧ble

indefatigable (comparative more indefatigable, superlative most indefatigable)

1. Extremely persistent and untiring.

   Synonyms: inexhaustible, relentless, tireless, unflagging, unsinkable, untiring, unwearying

   Antonym: (much less common) defatigable

   • 1749, Henry Fielding, “Containing Two Letters in Very Different Stiles”, in The History of Tom Jones, a Foundling, volume VI, London: A[ndrew] Millar, […], →OCLC, book XVIII, page 196:

     [...] But he was at the ſame Time an excellent Scholar, and moſt indefatigable in teaching the two Lads.

   • 1816 June – 1817 April/May (date written), [Mary Shelley], chapter I, in Frankenstein; or, The Modern Prometheus. […], volume I, London: […] [Macdonald and Son] for Lackington, Hughes, Harding, Mavor, & Jones, published 1 January 1818, →OCLC, page 39:

     He was respected by all who knew him for his integrity and indefatigable attention to public business.

   • 1895–1897, H[erbert] G[eorge] Wells, “Friday Night”, in The War of the Worlds, London: William Heinemann, published 1898, →OCLC, book I (The Coming of the Martians), pages 54–55:

     All night long the Martians were hammering and stirring, sleepless, indefatigable, at work upon the machines they were making ready, and ever and again a puff of greenish-white smoke whirled up to the starlit sky.

• indissuadable