From CS Lewis, in Mere Christianity:
People ask: "Who are you, to lay down who is, and who is not a Christian?": or "May not many a man who cannot believe these doctrines be far more truly a Christian, far closer to the spirit of Christ, than some who do?" Now this objection is in one sense very right, very charitable, very spiritual, very sensitive. It has every available quality except that of being useful. We simply cannot, without disaster, use language as these objectors want us to use it. I will try to make this clear by the history of another, and very much less important, word.
The word gentleman originally meant something recognisable; one who had a coat of arms and some landed property. When you called someone "a gentleman" you were not paying him a compliment, but merely stating a fact. If you said he was not "a gentleman" you were not insulting him, but giving information. There was no contradiction in saying that John was a liar and a gentleman; any more than there now is in saying that James is a fool and an M.A. But then there came people who said - so rightly, charitably, spiritually, sensitively, so anything but usefully - "Ah but surely the important thing about a gentleman is not the coat of arms and the land, but the behaviour? Surely he is the true gentleman who behaves as a gentleman should? Surely in that sense Edward is far more truly a gentleman than John?" They meant well. To be honourable and courteous and brave is of course a far better thing than to have a coat of arms. But it is not the same thing. Worse still, it is not a thing everyone will agree about. To call a man "a gentleman" in this new, refined sense, becomes, in fact, not a way of giving information about him, but a way of praising him: to deny that he is "a gentleman" becomes simply a way of insulting him. When a word ceases to be a term of description and becomes merely a term of praise, it no longer tells you facts about the object: it only tells you about the speaker's attitude to that object. (A 'nice' meal only means a meal the speaker likes.) A gentleman, once it has been spiritualised and refined out of its old coarse, objective sense, means hardly more than a man whom the speaker likes. As a result, gentleman is now a useless word. We had lots of terms of approval already, so it was not needed for that use; on the other hand if anyone (say, in a historical work) wants to use it in its old sense, he cannot do so without explanations. It has been spoiled for that purpose.
Now if once we allow people to start spiritualising and refining, or as they might say 'deepening', the sense of the word Christian, it too will speedily become a useless word. In the first place, Christians themselves will never be able to apply it to anyone. It is not for us to say who, in the deepest sense, is or is not close to the spirit of Christ. We do not see into men's hearts. We cannot judge, and are indeed forbidden to judge. It would be wicked arrogance for us to say that any man is, or is not, a Christian in this refined sense. And obviously a word which we can never apply is not going to he a very useful word. As for the unbelievers, they will no doubt cheerfully use the word in the refined sense. It will become in their mouths simply a term of praise. In calling anyone a Christian they will mean that they think him a good man. But that way of using the word will be no enrichment of the language, for we already have the word good. Meanwhile, the word Christian will have been spoiled for any really useful purpose it might have served.
The word feminist has always had a variety of meanings. When writers, historians, and social scientists try to make distinctions such as First Wave, Second Wave, and so forth, they are trying to tease apart the many meanings and impose some structure on them so that we may meaningfully discuss concepts. They (sometimes) know such distinctions are arbitrary and inexact, yet accept this in order that we may use the terms at all. Yet by describing the differences as a chronology - or even a development - I think they miss widely. It has been a loaded, and therefore imprecise word from the start. Many of the arguments about feminists and feminism have come down to these different understandings. "Oh, if that's all you mean by feminism, then I don't disagree. I was thinking of the type of woman..."
And ah, there we have it. Both men and women use the word to reference a picture of a woman they hold in their head, in addition to whatever strictly denotative meaning they hold. A type of woman. This may be positive, negative, or mixed, but we are never entirely free of that more emotional and social meaning. (Remember here my prejudice that liberal reasoning is largely social, conservatives less so. Both conservatives and liberals reason emotionally.) This is not merely a meaning imposed on others. Way back in the early 70s, a woman who described herself as a feminist, or not a feminist, or kind of a feminist, was not only talking about a set of abstract ideas, she was saying that she was smart/ambitious/modern/strong or calm/agreeable/traditional/ or any of a hundred combinations. A lot of time was spent explaining, which could sometimes make things worse.
It was a discussion about what women should be like and how they should be treated, and as a derivative, what men should be like and how they should be treated. Of course everyone took it personally, and still does. There were dozens of drivers that could swing a person one way or the other. The idea that women have been treated unfairly and this should stop was foundational for man. The observation that the most visible activists rather obviously had personal issues and some hated men affected others strongly. (Activists for anything are more likely to have "issues" and to hate someone. That is true of me when I act as an activist, so I can hardly blame others.) "Well, I think women should have equal pay for equal work but I don't hate men or anything" was close to a cliche. And not a bad one, really, as cliches go. It was a way of quieting the discussion so that people could move on to more productive conversation.
The strident antifeminists, especially the male ones, often clearly had personal issues leaking out of their comments as well. That is still true, and it makes even women who don't necessarily define themselves as strongly feminist crazy. So, still angry that your wife divorced you, eh, Chuck?
Women wanted to be like their mother. Or they very much did not want to be like their mother. Or they wanted to please/displease their father or that prince of a brother who kept getting all the glory. They wanted to make sure it was advertised that they wanted to get married, and further, that they wanted to have children. Or not have children. Or have them later, after their careers were established. Some liked the specialness of how women were treated in some situations, some hated it, most had mixed feelings. Men advertised how they weren't one of those terrible MCP's while simultaneously advertising that they were just fine with being good providers, and protective and brave and all that. Traditionalist parents found they were pleased with their daughter's achievements and incensed at her obstacles; some women were shocked to find that their whole outlook changed after having children, and later even more shocked to see how schools treated their sons, when they had been taught to expect that it was their daughters who were at risk.
How one felt about abortion, and laws about abortion, sliced through ideas of identity with a double-edged sword, and that was in turn influenced by unspoken but obvious attitudes as to whether having children was even valuable. In contrast to the idea that having children is the most important thing one can do.
We try. Most of us try to have some clear meaning for the word. Except for me. I have little idea what the word means and haven't used it for decades.