Since canonical might be confusing, and faq can't we just take something that is less confusing? E.g. oap for Often Answered Posts¹
But essentially any word that is not a common unix-command nor anything else often used in the Unix/Linux environment will do.
The people doing the searches would have to remember this of course and the tag description clear enough to make sense to people that come across it and are wondering what the tag is for.
Another thing to consider is what to do if such a canonical question already has the maximum of 5 tags.
¹ Originally I considered Frequently Answered Posts, I don't think that anyone would have problems remembering a tag that is an acronym of that, but it might not give the right impression to some visitors