The noun of supercilious: the quality of behaving as though other people matter less than you do. It names the attitude itself, so you can talk about it as a thing — the superciliousness of the staff, a hint of superciliousness in her voice, 'I could not stand his superciliousness'. It is uncountable: no 'a superciliousness', no plural. It shows up most when someone is complaining about, or analysing, a person's manner — a review of a restaurant, a character study in a novel, a complaint about how a clerk treated you. Like the whole family, it is formal and mostly written; in speech people would say 'his attitude' or 'the way he looks down on everyone'. Be aware it is a long word even for native speakers, and a heavy one to drop into a sentence — writers often prefer the adjective and rework the sentence around it.

傲慢、目中無人的態度（指那種瞧不起人的姿態本身，不可數）