ETYM Latin auxiliarius, from auxilium help, aid, from augere to increase.
Functioning in a subsidiary or supporting capacity; SYN. subsidiary, supplemental, supplementary.

1. An auxiliary person, group, or device; specifically; a member of a foreign force serving a nation at war; a Roman Catholic titular bishop assisting a diocesan bishop and not having the right of succession — called also auxiliary bishop
2. An auxiliary boat or ship
3. An auxiliary verb