Trademarks are the legal framework we use to protect phrases like this. In 1999, OSI applied for, and was denied, a trademark on the phrase "Open Source".[1] Perhaps there is a moral argument to be made to this effect, but there is not a legal one.
The entire dictionary is nothing but consensus on terms with no trademarks (and from which government?) anywhere.
OSI merely presents a definition as a service, for others to have something already thought-out to refer to rather than have to write a 10 page definition every time someone wants to refer to the concept.
It is well established by now, and the only people trying to argue about it are simply uneducated or have some deliberate agenda where they somehow benefit from artificially clouding an issue that has already gone through a process of being hashed out and recorded long ago. There is no reason to give them any air.
I'm not trying to make either a moral or a legal argument, only to warn against using the term in a way that is liable to cause confusion or needless antagonism.
[1]: https://opensource.org/pressreleases/certified-open-source.p...