Definition of indefatigable:

showing sustained enthusiastic action with unflagging vitality

Synonyms of indefatigable:

tireless, unflagging, unwearying, persistent, untiring, persevering, dogged, steadfast, determined, unfaltering, energetic, diligent

Opposite/Antonyms of indefatigable:

lazy, weary, work-shy, tired, lethargic, idle, fatigued, clean, clear, indolent, shiftless

Sentence/Example of indefatigable:

The fame of Claude Lorraine is partly explained by his indefatigableindustry.