unflagging

Adjective

• unceasing
  • unfailing loyalty
    
  • unfailing good spirits
    
  • unflagging courtesy
    

• showing sustained enthusiastic action with unflagging vitality
  • an indefatigable advocate of equal rights
    
  • a tireless worker
    
  • unflagging pursuit of excellence
    

Related words

• Synonyms: 
  unfailing , indefatigable , tireless , unwearying