indefatigable
1. [ adjective ] showing sustained enthusiastic action with unflagging vitality
Synonyms: tireless unwearying unflagging
Examples:

"an indefatigable advocate of equal rights" "a tireless worker" "unflagging pursuit of excellence"

Related terms: energetic
Similar spelling:   indefatigably
  indefatigability
  indefinable
  indefensible
  indefeasible