[n] a construction that is part of a sentence but not essential to its meaning and can be omitted without making the sentence ungrammatical
[n] something added to another thing but not an essential part of it
[n] a person who is an assistant or subordinate to another
[adj] of or relating to a person who is subordinate to another
[adj] 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"