1. indefatigable, tireless, unflagging, unwearying

showing sustained enthusiastic action with unflagging vitality

Example Sentences:
'an indefatigable advocate of equal rights'
'a tireless worker'
'unflagging pursuit of excellence'

Synonyms

• indefatigable
• tireless
• unwearying

2. unfailing, unflagging

unceasing

Example Sentences:
'unfailing loyalty'
'unfailing good spirits'
'unflagging courtesy'

Synonyms

• unfailing