Antonyms of professional:
amateur, nonprofessional, unprofessional, unpaid, amateurish, recreational, lay, blue-collar, inexpert, unskilled.
Examples of usage:
  1. " On professional business, my dear Martin; strictly on professional business; and I promised my girls long ago that they should accompany me.
    "The World's Greatest Books, Vol III", Arthur Mee and J.A. Hammerton, Eds..
  2. This was my last public appearance as a professional actor.
    "The Chronicles of a Gay Gordon", José Maria Gordon.
  3. Suppose we leave professional secrets alone, eh?
    "The Man with a Shadow", George Manville Fenn.