Where does the word “supercilious” come from and What does supercilious mean?

Actually the Latin source, supercilium, means the eyebrow, from super, above, and cilium, eyelid.

But the haughty man who looks contemptuously at those whom he regards as inferiors, inevitably looks at them with his eyebrows raised.

The old Romans were aware of this characteristic lifting of the brows in expression of scorn, and even with them superciliosus denoted an air of disdain.