If I understand him correctly, I disagree with CS Lewis that the practical meaning has left the use of the term. It's simply changed...as all language does, given a long enough timeline. Reading up quickly on the etymology, even his own definition is too vague depending on which time period we're using as the context. Apparently "gentleman" denoted something even more specific than his definition.
in its original and strict signification, denoted a man of the lowest rank of the English gentry, standing below an esquire and above a yeoman.
I am not an expert in linguistics by any means, but per the small variety of courses I've been exposed to, one of the hallmarks of language is its tendancy to change over time. I agree with the idea that terms have to have a common basis or it doesn't do much good at conveying the meaning, but ultimately I don't think we can control others' usages because of my understanding on how people acquire and apply meaning. We can invite them to share our own application and understanding, but it's a "leading horse to water" situation.
In my TESL courses the material was presented by way of the Constructivist
lense wherein the meaning of things is developed largely through the process of application. I rather like this approach because I think it reflects the natural way things like semantics arise. This doesn't mean the term "cat" can mean "dog" so much as "cat" will mean whatever it is the user has acquired through the process of learning, and that the meaning will naturally shift or refine over time as the process continues. With this in mind, it becomes less important to stress precision of terms than competence in applying and explaining one's comprehension...which relates somewhat to what Chris said earlier regarding the need for more qualifiers. Acquisition of meaning/semantics is something that is necessarily filtered through the individuality of the agent applying them.
Hopefully I expressed the above well enough (and that I even understand it well enough, for that matter), but based on it, I believe the term Aikido will necessarily be different based on who is practicing it since their individual complexities will affect their comprehension and expression of it. This is why for me, the term usually just denotes the kind of jujutsu training inspired by O Sensei's practice and teaching. This leaves a lot of room for personal interpretation based on personal proclivities, allowing me to refer to many practices that often look radically different.