1. Without official authorization
   - on the side 
2. Not in an official capacity
   "unofficially, he serves as the treasurer"

See also: unofficial

Antonym: officially

• fleetly
• fleetness
• Fleming
• Flemish
• Flemish dialect
• Flemish-speaking
• flense
• flesh
• flesh and blood
• flesh fly
• flesh out
• flesh wound
• flesh-colored
• flesh-coloured
• flesh-eating
• fleshed
• fleshed out
• fleshiness
• fleshly
• fleshpot
• fleshy
• FLETC
• fletch
• fletcher
• fleur-de-lis