I've mentioned this in chat before, but it seems like higher academia tried, and failed to redefine the word grammar to have a more restrictive set of categories in the late 19th century through to the early 20th. You can see evidence of this in the Century Dictionary and Cyclopedia, the earliest printings of the Oxford English Dictionary and
At least part of it is predicated on the notion that only spoken language is real language because it is the core component of what constitutes language , with writing being an optional representation, as argued by grammarian Leonard Bloomfield. I hypothethize that part of it may also be based on etymological grounds (language is derived from the latin lingua for tongue). If there is an etymological component, it neglects to note that the gramma in grammar is essentially derived from the greek word for letter/character.
Historically speaking, the categories of grammar are include etymology (as in the overall art of word derivation), prosody, orthoepy (if not considered a part of prosody), orthography and syntax. Moreover, the word is somewhat polysemous, so in addition to these categorical arts there are definitions of it such as optimal use of a language, et cetera. You can see this in sources such as A Grammar of the English Tongue by Samuel Johnson, or The Grammar of English Grammars by Goold Brown. I could list more sources, but for the purposes of meta, I trust that suffices, so for the sake of brevity and convenience I won't. This is also only accounting for the primary definition of the word, as the word is also somewhat polysemous, and has also been used to describe optimal usage of language and things pertaining to grammar, such as grammar books.
I know that some of you are quite attached to the word grammar as specifically meaning syntax and morphology, but this not only neglects most of the word's overall historical usage in the English Language, but also the common definition of the term as held by the common man, which was likely been forced upon them as schoolchildren. Worst of all, it also leaves people who have use of the broader sense of the word with a lexical gap. This is contrary to the tenets traditionalism, populism, and the only justification for this is basically just because a few pedants say so.
Now you may disagree, and if so we don't have to settle what the word grammar should mean here. I only wish to touch upon why people find this so confusing and why the effort to make people use the grammar tag "correctly" may be so futile.
Nevertheless, despite however much I may personally disagree with her conclusion, Snailboat made a rather compelling case that grouping syntax and morphology together can be useful in her answer to What is meant by "grammar"? over at English Language Learners. Syntax and etymology are intrinsically linked, because if you change the termination of a word or reduce it to its root form, you may change its part of speech which would necessitate different syntactical treatment, which is to say nothing of the fact that affixes are generally only applicable to one or two parts of speech. We are not the only ones to note how problematic the word grammar is though, and a neologism meant to refer strictly to the interaction of these two categories exists, which is morphosyntax.
The Solution I Recommend
We do not need a category in our tag taxonomy as broad as grammar can be when interpreted broadly. Even when interpreted narrowly it is more useful for questions to be tagged with syntax or morphology if they only pertain to one of the two domains.
The grammar tag as it is presently defined only makes sense if a question specifically regards the interaction of syntax and morphology. Therefore, I propose that we should create a morphosyntax tag, and make grammar a synonym of it.
Being a technical word invented to serve a specific technical purpose, morphosyntax is a word that will probably appeal to serious linguists. It does not come with the connotations of the word grammar, and its construction deters misuse, especially by those people who do not even know what it means. This solution also helps us to avoid being bereft of tags to help isolate the specific nature of the question. We also don't need to consult upper management to create a tag synonym.
The only thing I really dislike about this solution is that a new master tag would inherit all of the mistaggings of the old one, and grammar is one of our most used tags so correcting the tag taxonomy would require an extensive effort. However, this is something we could fix with enough time and effort, and it wouldn't be all that much worse than it is now, especially since we don't even have a morphosyntax tag at the moment.
Also, grammar shouldn't be moved to the don't ask section of our scope, because questions regarding grammar, in both its broader and narrower interpretations are, at least for the most-part, on-topic. We should simply delete the word grammar from the list of accepted topics, and replace it with separate syntax and morphology bullet points, in both the tour and our help center's scope.