1. Showing sustained enthusiastic action with unflagging vitality
   "unflagging pursuit of excellence"
   - indefatigable, tireless, unwearying 
2. Unceasing
   "unflagging courtesy"
   - unfailing

See also: constant, energetic

• gun down
• gun emplacement
• gun enclosure
• gun for hire
• gun moll
• gun muzzle
• gun pendulum
• gun rest
• gun room
• gun smoke
• gun trigger
• gun turret
• gun-shy
• gunboat
• gunboat diplomacy
• guncotton
• gunfight
• gunfighter
• gunfire
• gunflint
• gung ho
• gunge
• gunite
• gunk
• gunky