WordWeb Online

1. Not paid
   "unpaid wages"; "an unpaid bill"
    
2. Without payment
   "the soup kitchen was run primarily by unpaid helpers";
   - volunteer
    
3. Engaged in as a pastime
   "unpaid extras in the documentary";
   - amateur, recreational

See also: buckshee [Brit, informal], complimentary, costless, courtesy, due, free, gratis, gratuitous, non-paying, nonprofessional, outstanding, owing, pro bono, rent-free, uncompensated, undischarged, unsalaried, voluntary

Antonym: paid