1) Amateur 2) Buckshee 3) Costless 4) Due 5) Gratis 6) Late 7) Nonprofessional 8) Owing 9) Uncompensated 10) Undischarged 11) Unsalaried 12) Voluntary 13) Volunteer 1) Buckshee 2) Charitable 3) Checkless 4) Complimentary 5) Costless 6) Engaged in as a pastime 7) Free 8) Gratis 9) Gratuitous 10) Like accumulated bills 11) Like outstanding debts 12) Like some bills 13) Like some internships 14) Like some leaves 15) Like some outstanding bills 16) Like volunteer work 
[adj] - without payment 2. [adj] - not paid
unpaid 1. Without payment. 2. Awaiting payment or settlement; such as, unpaid bills. 3. Not yet in receipt of payment for work done. 4. Working without wages or a salary. 5. Serving without pay; unsalaried: 'We worked as unpaid research assistants.'
volunteer(a) adjective without payment; `the soup kitchen was run primarily by unpaid helpers`; `a volunteer fire department`