That's the thing, the definition of the word was never changed. Never once have Libertarians declared that it has. The only people claiming that the word's definition has changed have been the right wing Proeprtarians that over the course of the last 50 or so years have attempted to use it as a mask for their own ideology which incidentally would actually result in the opposite of what Libertarianism stands for. That is, putting liberty above all. Corporations don't give a shit about your personal liberty. All they care about is the status quo and making as much money as possible.

The fact that the definition of 'Libertarianism' has never been changed by Libertarians is evident by the fact that ideologies such as Libertarian Communism still exist. (Libertarian Communism was one of the original names for Anarcho-Communism in case you were wondering.)

If you've read my other comments here then you would know that Libertarianism has always been synonymous with Anarchism for the most part and that's why it's used by Anarchists when describing things like Libertarian Socialism.

To put the usage f the word into perspective, say that I'm the color red and I develop an ideology around my own beliefs and happen to call it 'Redism' or something. Then you come around and like how 'Redism' sounds, so you try and use it to describe yourself despite you being the color blue and 90% of the beliefs held by 'Redism' are actually contradictory to your own beliefs. Then the problem arises of 'Redists' questioning your usage of the word and you use the excuse of "Oh, words just change definition over time, deal with it." Do you see what I mean? If a group of individuals all based around a certain ideology use a certain term to describe their beliefs you cannot simply walk up and expect to use the term to describe something completely different. Especially since the word has been used to describe their beliefs for over 150 years before you started using it and your usage is only limited to only a few countries whereas the rest of the world still used the original meaning. I digress...

What I'm trying to say is that Libertarianism has always meant for the past 200 years hasn't changed just because a bunch of Propertarians have decided to use the term for their own benefit over the course of the last 50 years.

EDIT: And how exactly do u "steal" a word?

Honestly, I don't know. I think that 'reapproproate' would better describe this situation rather than 'stealing'.