(I apologize that there have been similar questions before, but I'm not sure adding to them would be best here. Perhaps the most reasonable option would be to add to this question, but it is rather old, and adding stuff to the end of a long list will tend to bury it, which is the opposite of what I'm hoping to achieve here.)

I have recently been perusing tags & questions & related materials, and I thought it might be worthwhile to try to bring some things to the community's attention. It started when I edited this question, which is tagged with both lme and multilevel. Neither of these tags has a wiki (excerpt or full), and they seem like synonyms to me. I tried to map [multilevel] (which seems less used) to [lme], but the system wouldn't let me, as I don't have 5 upvotes on the tag. So I thought I would raise the issue here, and if enough people agree, perhaps we can get this done somehow. In addition, however, I notice that there are a few pending synonyms that don't seem to be getting any votes either way, so I thought I might as well list several options as answers below and let people vote on them to drive attention and action on this issue. I would also like to encourage others who have additional suggestions to append them to this list (in that regard, note this recent question, as well).