Ironically libertarian was originally a synonym for anarchist, and was also stolen by the right.

One gratifying aspect of our rise to some prominence is that, for the first time in my memory, we, ‘our side,’ had captured a crucial word from the enemy . . . ‘Libertarians’ . . . had long been simply a polite word for left-wing anarchists, that is for anti-private property anarchists, either of the communist or syndicalist variety. But now we had taken it over…

– Murray Rothbard

Many still use the term “Libertarian Socialist” to specify they mean libertarian in the original sense.