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

See also: unofficial

Antonym: officially

• mesne
• mesne lord
• meso-
• Mesoamerica
• Mesoamerican
• mesoblast
• mesoblastic
• mesocarp
• mesocolon
• Mesocricetus
• Mesocricetus auratus
• mesoderm
• mesodermal
• mesohippus
• mesolithic
• Mesolithic Age
• mesomorph
• mesomorphic
• mesomorphy
• meson
• mesonic
• mesophyron
• mesophyte
• mesophytic
• mesophytic plant