adj. 25B6; adjective VIGOROUS, energetic, determined, resolute, enthusiastic, keen, zealous, spirited, dogged, tenacious, persistent, persevering, staunch; tireless, unflagging, unfailing, unfaltering, unwavering, indefatigable, unrelenting, unswerving; formal pertinacious.
UNTIRING
Meaning of UNTIRING in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012