Gay
Here’s an example. Way back when, gay meant “lighthearted, cheeky, colourful.” It became a sarcastic, disapproving euphemism for behaviour that society frowned upon, such as partying, drinking, and sexual activity without marriage. Homosexual people, who were forced by law and social norms to live hidden lives or on the fringes of society, borrowed the word as a joke and secret self-identifier. When law and society changed, that meaning became public.

Gay: really?
But gay isn’t always a neutral synonym for homosexual. Hang around any schoolyard and you’ll hear some kid calling someone, or something, “gay”—in a tone that says, “stupid, not normal, something to be disdained.” Suddenly, stepping forward to claim that label for yourself seems like a bad idea.

Words as power tools
Words have power; even more so when people with power use them—the popular group, the strong ones, the richest or most numerous or privileged ones. But in the end, words are tools, and we can decide how to use them—and be used by them.