adjunct - a construction that is part of a sentence but not essential to its meaning and can be omitted without making the sentence ungrammatical

incidental, incident - (sometimes followed by `to') minor or casual or subordinate in significance or nature or occurring as a chance concomitant or consequence; "incidental expenses"; "the road will bring other incidental advantages"; "extra duties incidental to the job"; "labor problems incidental to a rapid expansion"; "confusion incidental to a quick change"