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

See also: unofficial

Antonym: officially

• serry
• Sertoli cell
• Sertoli's cell
• sertraline
• Sertularia
• sertularian
• serum
• serum albumin
• serum disease
• serum globulin
• serum hepatitis
• serum sickness
• serval
• servant
• servant girl
• servant's entrance
• serve
• serve up
• serve well
• server
• server cluster
• server farm
• service
• service abroad
• service agency