1. useful
   1. unuseful
      1. unusefulness
2. usable
   1. usability
   2. usably
   3. unusable
3. useless
   1. uselessness
4. disuse
5. used
   1. unused
6. reuse
   1. reusable
   2. reusablity
7. using
8. user
   1. username
   2. userid
   3. userinfo
   4. userkit
9. usage