Subservient or subordinate, like a handmaid; auxiliary.

A proceeding which is auxiliary or subordinate to another proceeding. In probate, a proceeding in a state where a decedent owned property but was not domiciled.

supplementary ( ancillary data with regard to SeaWiFS refers to data from other sources that is used in data processing)

Additional services (other than room and board charges) such as X-rays, anesthesia, lab work, etc. Fees charged for ancillary care such as X-rays, anesthesia, and lab work. This term may also be used to describe the charge made by a pharmacy for prescriptions which exceed the health insurance plan's maximum allowable cost (MAC).

Fees above and beyond room and board associated with hospitalization. May include x-rays, lab work, anesthesia and other procedures. May also refer to actual fee charges. This term can also include prescriptions which go beyond an insurance plan’s Maximum Allowable Cost (MAC.)

Services that are not classed as Medical or Hospital. (e.g. Dental/Optical/Physio etc.)

relating to something that is added but is not essential; "an ancillary pump"; "an adjuvant discipline to forms of mysticism"; "The mind and emotions are auxilliary to each other"

An ancillary activity is something that is added and related to a larger main activity that improves it. For example, if the main work of an organization is to improve the environment, then ancillary activities might include educating the public about pollution, or persuading the government to make laws against polluting.184

Supporting the main purpose of a development. A local shop may be ancillary to a large housing development.

Tests and procedures ordered by healthcare providers to assist in patient diagnosis or treatment (radiology, laboratory, pathology, etc.).

accompanying