on_the_side
1. [ adverb ] without official authorization
Synonyms: unofficially
Examples:

"he had made some money on the side"

Related terms: unofficial unofficial
Similar spelling:   on_the_sly
  on_the_spot
  on_the_quiet
  on_the_QT
  on_the_go
  on_the_job
  on_the_Q.T.
  on_the_hook
  on-the-scene