Otherwise, I can say something like this and expect you to understand me: Most people believe that an onlooker underhandedly ignores an omphalos, but they need to remember how non-chalantly the cigar about an espadrille laughs out loud. When a menagé à trois for a labyrinth rejoices, a starlet living with a clodhopper feels nagging remorse. An unsightly impresario is darling. When the surly menagé à trois starts reminiscing about lost glory, a curmudgeonly bubble ceases to exist.
Or I can redefine water to mean any clear liquid, including sulfuric acid, and sell that to you, and claim you should've understood what I meant when you die.
The words "open source" have a plain pre-existing meaning. "Water" does not.
Now to go ahead and make your argument for you - this use of the term open source might be like if I went ahead and sold you (having to force this a bit, since I've failed to find a good example of a noun) insurance against kicking the bucket, and then I tried to define it as insurance against literally kicking buckets. Possibly you can find a better example, but that's the best I could come up with and
- "the bucket" clearly distinguishes the term from being merely descriptive
- Selling insurance against kicking buckets makes no sense, unlike "open source software" where "open" means "anyone can look at it"
- Kicking the bucket is a phrase with a much longer history than OSI defined open source software.
Option a) Makeup a non-generic not already in use term and trademark it.
Option b) Just say "licensed under <well_known_license>".
What you're required to do to get the exclusivity you're looking for is well established in the rules we are all required to play by known as "the law".