Supercilious people think very highly of themselves, more highly than of others. If your sister tends to act snobby and superior, you can describe her as supercilious.

You might expect Nobel Prize winners to be supercilious — after all, they've reached the very heights of their profession. But one-on-one, your famous physics professor might be humble and fun to talk to, anything but supercilious. Most often, it's people who have no right to be arrogant, rude, and holier-than-thou who behave in the most supercilious ways. The Latin root supercilium means "haughty demeanor," but also "eyebrow" — as in an eyebrow raised in a haughty, supercilious expression.

Definitions of supercilious

adj having or showing arrogant superiority to and disdain of those one views as unworthy

“his mother eyed my clothes with a supercilious air”
disdainful, haughty, imperious, lordly, overbearing, prideful, sniffy, swaggering
feeling self-respect or pleasure in something by which you measure your self-worth; or being a reason for pride

adj expressive of contempt

“curled his lip in a supercilious smile”
sneering, snide
tending to (or intended to) detract or disparage