Mark Twain often puts it best: “The difference between the right word and the almost right word is the difference between lightning and a lightning bug.” If I were to translate into my version of English, I'd say “between fireworks and a firefly”. But somehow that's not as good.

Either way, as a writer's creed, it's hard to beat. The English dictionary is longer than any other. Our language allows us to choose from the most astonishing array of ways to express our observations, ideas, emotions. And it leaves us to drown if we select the wrong route. But, if our writing aims to challenge power – and, to steal some words from another figure who is over-quoted, “all art is propaganda” - then it is crucial to think not just about the poetry in a word, but also the politics.

Language is perhaps the most obvious of all social constructs. And if it exists, as it does, in a society where power is spread unevenly, we can assume this will be reflected in its use. This was hinted at in a recent article on OurKingdom in which a Scottish contributor asked the English what word it is that we Scots use when we wish to be unkind about our Southern neighbours. His point was that there isn't one.

I stumbled upon it again when, in an interesting piece on multiculturalism (not yet published), a writer used the word “indigenous” to describe white people in Britain whose families have mostly lived here for many generations. Does the fact that this word is used by the far right to make bigoted points mean that it is now a problem to use it when making analytical ones? And, if so, what other term can be used which isn't a lightning bug to Twain's lightning? This, I suppose, is a standard difficulty with our “often clumsy negotiation towards a formally inclusive language”.

The question was raised again when I had lunch with another of the openDemocracy crew. I said that 'socialist' describes my beliefs about how the economy ought to be run. He doesn't use the label. Yet our views on any practical matter about wealth, ownership, trade and resources would be hard to distinguish. The difference is that, for him, the word is poisoned by its association with statists and Stalinists. I think it might be worth reclaiming.

And that leads to an interesting question – reclaiming from whom? This is better answered, I feel by turning to recent news. David Cameron, ahead of his speech to a wilting Conservative party conference, has announced that he has changed his mind. He is now a feminist. The quote is a marked contrast with his female predecessor. Mrs Thatcher, we are often told, described the school of thought as “poison”.

And if anyone has thought about the ways power can warp words as much as words can challenge power, it's the feminist movement. Cameron hasn't changed his beliefs, just his label. Well, that, and the strategy with which he attacks some of his most vocal critics.

There was a point when the plan used by the powerful against the feminist movement was to do more subtly what Thatcher did explicitly - make their name toxic. Every stereotype that might flicker into your mind when you hear 'feminist' was beamed there by this dynamic. The powerful took a word forged in struggle and rewrote its meaning.

At the same time, there were debates among the women fighting gender oppression. In 1983, Alice Walker first described her beliefs with the word 'womanism'. 'Feminism', she felt, was white. It didn't sufficiently express the experience of black women. In the complex web of privilege (for which the word kyriarchy has also been invented), it was white women who had been able to define the meaning of the name of the movement. Sometimes, if you want to set the forest on fire, you need to make your own lightning.

Thirty years later, the word 'feminist' is being challenged in a different way. Cameron's deeds devalue the sorts of work women tend to do, and force more and more women into poverty. If the power in the word “feminist” can't be boiled away by binding it to those most loathed by the Daily Mail, perhaps the powerful can dilute it through co-option?

The word socialist has gone through a similar trajectory. In the USA, a couple of years ago, there was a poll. It asked Americans what they felt about various political terms. Among 18-29 year olds, more had positive feelings about 'socialist' than did about 'capitalist'. Within living memory of McCarthyism, this is remarkable. But I don't believe it is because young Americans have considered the merits or demerits of democratic control of the means of production. 

Here's what I think has happened. Republicans – stuck in the Cold War – assume the word will kill all it touches. As a result, they have used it to describe their centrist opponents - Obama and Clinton. But a generation which couldn't spell out USSR doesn't see 'socialism' as a synonym for 'traitor'. They assume it accurately defines the politicians who are branded with it. And so they adopt it. In this context, David Cameron calling himself a feminist isn't really any different to Clinton's apostle, Tony Blair, calling himself a socialist. 

So how should those of us who wish to challenge authority with words react when they are slanted, pulled apart, warped, or sometimes, stolen by the powerful? Should we just choose new ones? Well, sometimes. Certainly, if our ideas are new, they should be properly christened. If a word is contorted into a weapon of oppression against those with less power than us, we must drop it. 

But it's worth remembering that, as gravity will always act on mass, power will always act on language. And, under Newton's second law, it will push back most forcefully against our best labels. The difference between the right word and the almost right word is the difference between lightning and a lightning bug. If we allow each one only to strike once before its force is neutralised, we'll have to invent a whole new language.