/ ˌɪndɪˈfætɪgəbl; NAmE / adjective
( formal , approving ) never giving up or getting tired of doing sth :
an indefatigable defender of human rights
► in·defat·ig·ably / ˌɪndɪˈfætɪgəbli; NAmE / adverb
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WORD ORIGIN
early 17th cent.: from French , or from Latin indefatigabilis , from in- not + de- away, completely + fatigare wear out.