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

See also: constant, energetic

• funny story
• funny wagon
• funrun
• Fuqra
• fur
• fur coat
• fur hat
• fur seal
• fur-bearing
• fur-piece
• furan
• furane
• furbelow
• furbish
• furbish up
• furcate
• furcation
• furcula
• furcular
• furfural
• furfuraldehyde
• furfuran
• furioso
• furious
• furiously