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

• undershrub
• undershrubs
• underside
• undersides
• undersign
• undersigned
• undersigning
• undersigns
• undersized
• underskies
• underskinker
• underskinkers
• underskirt
• underskirts
• undersky
• undersleeve
• undersleeves
• underslung
• undersoil
• undersoils
• undersold
• under someone's wing
• undersong
• undersongs
• underspend