Okay normally I'm on the side of "words mean whatever we need them to mean".
but guys, I don’t like the suggestion that it’s what is happening here. Being unfamiliar with the term, and guessing its meaning based on vibes, doesn’t mean you have equal authority on whether it’s “correct” with the community who actively use this word in a technical sense.
please do consider that if you haven't been exposed to the word in the context it's used in, "both are correct" and "you can interpret it differently" and “there is no right or wrong answer” and “it feels like it SHOULD be X” cannot be a fully realised take. Sure, linguistics recognises there are rules in which meaning changes - but “laypeople being unfamiliar with the word, and liking vibes better” isn’t one of them.
You can do that with most words, especially slang, and shape them to the needs of the majority, but this isn't like... a fanfiction word, invented for fanfic and, like, solely used for injured hockey players where it doesn’t matter if the injured limb swaps sides 4 times in a sex scene and phases through a stomach. It is, in its context, a bit more load-bearing (ha) than that.
It's fine to be unfamiliar with the context, and it's fine for words to change, but do just take a quick second to hear it in a native sentence!
One of the most common ways of using this word is to assess four-legged animals. "Favouring" is a specific grouping of behaviour - a hesitancy in gait, stiffness, reluctance to put weight on a limb. It’s often inconsistent, as the animal tries to compensate or conceal the pain. It may not be a full limp or obvious lameness, since prey animals especially will actively try to conceal this; favouring is a subtle reluctance, and a useful word for a very specific recognisable behaviour that the animal is usually trying to lie about. (That’s probably why it’s used in romance fiction, as it’s an interestingly romantic and stoic way to react to pain, and doesn’t mean the limb is inconveniently disabled. A fictional character favouring a wounded leg can wince attractively when it’s jostled, but it doesn’t matter too much if the author forgets and has them run to the door suddenly - “favouring” isn’t incompatible with “running” in horses either.)
The sentence “Favouring the off hind” is equestrian jargon: it means “pain behaviour on the back right leg.” It does not mean “opposite-pain in the not-on deer” and is not confusing in its professional register.
If you've only vaguely heard of "myeloma", and most people in a poll are guessing it's a skin cancer, that doesn't mean that myeloma and melanoma can now readily collapse into the same word - they're under active use in their native contexts, where the people frequently using them do need to communicate the difference between skin and blood cancer.
A poll of laypeople misunderstanding “myeloma,” or non-horse-people misunderstanding “favouring,” isn’t quite enough to indicate a full semantic shift and change of meaning of the term. The community that uses the term “favouring” in the context of “limb injury” - vets, farriers, farmers, commentators, equestrians - knows what it means and uses it consistently in the same way. They’re not confused. because to them, it isn’t a vibesy, sex-scene-hand waving word. It’s a cluster of pain signals.
If you aren’t familiar with that usage, then that’s really more about your own lack of familiarity. Not all interpretations DO carry equal authority, especially when one is just confusion/unfamiliarity. You just haven’t met it before, and that’s fine.
Tl;dr: I’m all for words changing meanings, but we shouldn’t be too quick to declare that when it’s based entirely on unfamiliarity and vibes-based readings.