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My sister is indefatigable or tireless in her efforts on behalf of the homeless. She volunteers at the shelter everyday and writes to her senator constantly with an indefatigable, endless determination. She never seems to tire of coming up with new ways to help. She is an indefatigable, energetic, and highly active defender of the rights of those who are in need.

Quiz: What does it mean to be indefatigable when you do something?

  • You seem to be able to do it without losing any energy.
  • You embrace it with all of your energy and drive.
  • You are devoted to worthy social causes.

Memory Hook

Big, Fat, and Undependable Don't tell me that a big, fat, and undependable soccer player will be indefatigable! How could he move that much weight around the field without getting exhausted?


  • The indefatigable pursuit of an unattainable perfection, even though it consists in nothing more than the pounding of an old piano, is what alone gives meaning to our life on this unavailing star. — Charles Peguy Charles peguy
  • The indefatigable Guggenheim, which already operates branches in Berlin and Venice, has plans for a 687 million building at the southern tip of Manhattan and is also casting its eyes on Brazil. —Newsweek
  • Perhaps one of the most striking impressions one takes from 'My Life in France' is of Child’s indefatigable attention to detail and insistence on an exact, careful approach to cooking. —The Christian Science Monitor
  • The research is nearly unanimous: Working out regularly, vigorously, and steadily over the years triggers a host of cardiovascular and muscular adaptations that together make you a better, stronger, more indefatigable version of yourself. —Men's Health

Word Ingredients

in- not
de- from
fatig weary, tire
-able handy, capable of

An athlete who is indefatigable is “not capable of tiring or wearying from” effort.

Word Constellation