Open source is not an ambiguous term. FOSS stands for “free and open source software”. It extends the word you claim is ambiguous with the word “free”. That word actually is ambiguous as in other cases it could mean “gratis” and not “it grants it’s users freedom”.
How is that better than the more established term with the very clear definition by the OSI? It’s okay if you mixed these terms up. I just don’t understand what you’re trying to do here.