Just a note, I just added tag wikis for alchemy and alchemist and cleaned up a few questions for each. I decided against synonymizing because a distinction was apparent in their emergent usage, and because it parallels the distinction we have between e.g. wizard and spellcasting.
Actually, for the most part, the emergent usage was pretty good: alchemist were for questions about a (usually Pathfinder) class by that name, and alchemy was for questions about the production and usage of alchemical items. I have codified this distinction in the tag wikis. Only a few questions needed to be edited to fit the scheme.
There are a couple of questions that have both tags, but they’re explicitly about creating or using alchemical items as a member of an alchemist class, so that seemed OK.
I did leave a dnd-4e question that was asking about the “Alchemist” feat and how it was used to produce certain items tagged with alchemy rather than alchemist, since despite the feat’s name it seemed much more appropriate to that tag.
Anyway, wanted to start a meta discussion about the tags in case anyone wanted to chime in.