According to dictionary.com
1. subordinate; subsidiary.
2. auxiliary; assisting.
And according to medterms.com
A perfumer might have an ancillary scent. Hopefully not an axillary one.
Axillary: Pertaining to the cavity beneath the junction of the arm and the body, better known as the armpit.
The word "axilla" was borrowed directly from the Latin. To the Romans, as to us, the axilla was just the armpit.
Further, the axillary artery is definitely not ancillary.
I'm glad I cleared that up.