from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Incapable or seemingly incapable of being fatigued; tireless. See Synonyms at tireless.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Extremely persistent and untiring.
from the GNU version of the Collaborative International Dictionary of English
- adj. Incapable of being fatigued; not readily exhausted; unremitting in labor or effort; untiring; unwearying; not yielding to fatigue.
from The Century Dictionary and Cyclopedia
- Not defatigable; incapable of being fatigued; not easily exhausted; not yielding to fatigue; unremitting in labor or effort.
- Synonyms Unwearied, untiring, tireless, unflagging, persevering, assiduous, persistent, sedulous.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. showing sustained enthusiastic action with unflagging vitality
Obsolete French indéfatigable, from Latin indēfatīgābilis : in-, not; see in-1 + dēfatīgāre, to tire out (dē-, intensive pref.; see de- + fatīgāre, to weary).(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin indēfatīgābilis ("untiring"), from in- ("not") + de- ("away") + fatīgō ("I tire"). (Wiktionary)