Failed to propose synonym:
Version specific synonyms can only be created by moderators
I want to suggest game-maker-studio-2 (11 questions) as a synonym of the main tag game-maker (420 questions). Reason is, GMS2 is just a new version of the engine, but that seems no different from merging unity5 questions in the main tag unity, or xna-4.0 into xna.
I think this is different from having separate tags for game-maker and game-maker-studio, because GMS1 and GMS2 are quite similar, and their differences involve only the actual engine implementation. On the other hand, pre-Studio versions (up to 8.1, I guess) are basically deprecated and no longer supported, thus we can expect nobody is going to ask a question about old, specific versions.
To sum up: GMS and GMS2 are different versions of the same software and basically expose the same functionalities. Since earlier versions are obsolete, we could merge everything into the game-maker main tag.