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

See also: unofficial

Antonym: officially

• iso-
• isoagglutination
• isoagglutinin
• isoagglutinogen
• isoantibody
• isobar
• isobaric
• isobilateral
• isobutyl nitrite
• isobutylene
• isobutylphenyl propionic acid
• isocarboxazid
• isochoric
• isochromatic
• isochronal
• isochrone
• isochronous
• isoclinal
• isocline
• isoclinic
• isoclinic line
• Isocrates
• isocurvature
• isocyanate
• isocyanic acid