Words, like the rest of the world, evolve. Here are some words whose original meanings you may not recognize. Source:
Egregious: It used to be possible for it to be a good thing to be egregious: it meant you were distinguished or eminent. But in the end, the negative meaning of the word won out, and now it means that someone or something is conspicuously bad — not conspicuously good.
Naughty: Long ago, if you were naughty, you had naught or nothing. Then it came to mean evil or immoral, and now you are just badly behaved.
Silly: Meanwhile, silly went in the opposite direction: in its earliest uses, it referred to things worthy or blessed; from there it came to refer to the weak and vulnerable, and more recently to those who are foolish.
Hussy: Believe it or not, hussy comes from the word housewife (with several sound changes, clearly) and used to refer to the mistress of a household, not the disreputable woman it refers to today.