tireless

Meanings

1. 1
   adj

   showing great energy and persistence without appearing to become tired

   The tireless professor worked through the day without asking for a rest.

Formed from tire ("to become weary") + -less. Tire in this sense is recorded from Middle English, though its deeper origin is uncertain. The suffix -less gives the literal meaning "without tiring," now usually applied to persistent effort or an energetic person.

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