ac·ces·so·ri·al /ˌæksəˈsoriəl, ˈsɔr-/
(a.)附屬的,從犯的
Ac·ces·so·ri·al a. Of or pertaining to an accessory; as, accessorial agency, accessorial guilt.
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accessorial
adj : something added that is nonessential but helpful;
"accessorial services included sorting and packing"