The adjective imperious means (1) arrogantly domineering or overbearing, or (2) regal. It’s synonymous with dictatorial, and it comes from the Latin imperium, which means extreme authority. Impervious means (1) incapable of being penetrated, or (2) unaffected.
Pervious is a real word, meaning open to passage, but it’s much rarer than its im- antonym.
Examples
Imperious is often used to mean masterly (which is different from masterful). This sense of imperious, which may come from a misinterpretation of the word as meaning without peer, is not quite in line with the word’s conventional definition. For example, these writers use imperious apparently without the negative connotations relating to arrogance:
The unstoppable Edwards has been in imperious form since returning from a self-imposed break … [Stuff.co.nz]
However, none of Kauto Star’s rivals would hold a candle to him at his imperious best. [Belfast Telegraph]
In these cases, a word like masterly would make more sense than imperious.
These writers use imperious well (with the negative connotations):
The mainstream media tells us so, with an imperious sneer. [Washington Post]
Those receiving public assistance … dislike being treated with contempt by imperious government officials. [Waterloo Record]
And these writers use impervious well:
He speaks with misplaced authority and received wisdom in a place that is far from impervious to manipulation. [Independent]
Indeed, he seems impervious to criticism of almost any kind except of his remarkable hairstyle … [Economist]
