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

See also: unofficial

Antonym: officially

• tangle orchid
• tangle with
• tanglebush
• tangled
• tangly
• tango
• tangor
• tangram
• Tangshan
• Tanguy
• tangy
• tanh
• tanistry
• tank
• tank car
• tank circuit
• tank destroyer
• tank driver
• tank engine
• tank farm
• tank farming
• tank furnace
• tank iron
• tank locomotive
• tank shell