ancillary /an-silˈə-ri or anˈsi-lə-ri/

1. Auxiliary
2. Supplementary
3. Subsidiary
4. Subordinate
5. (of computer equipment) additional in any way, not a necessary part of the computing process
6. Subserving
7. Ministering

An ancillary thing

• used-up
• useful
• useful arts
• useful life
• useful lives
• useful load
• useful loads
• usefully
• usefulness
• usefulnesses
• useless
• uselessly
• uselessness
• uselessnesses
• Usenet
• usen't
• user
• user-friendly
• user ID
• user IDs
• user interface
• user interfaces
• username
• usernames
• users