Over the past couple of months there have been quite a few suggestions about words classed as common that forumites thought should be rare. I haven't got around to answering most of these until now. I've concluded that the following words ought to be switched to rare.
tench
shad
hake
plaice
ling
hotted
phage
eglantine
aconite
pelf
schwa
twee
coopt
goober
mingy
Many of these are quite common in some parts of the world, but much less common in other English-speaking regions. Some of them are fairly uncommon everywhere.
I hesitated about a few of these. The letters for ling come up so frequently, that many players will probably be surprised if it comes up as rare. However, I'm resistant to the idea of treating words as common just because they're often seen in word puzzles. Twee is quite well known in Britain and Australia, but seems to be used much less frequently in the US, and many US dictionaries label it as British, or chiefly British. Mingy, on the other hand, does not have a regional label in most of the dictionaries I looked at, but it seems to be much less commonly used in America than in Britain. It looks like co-opt, with a hyphen, is more often used than coopt on both sides of the pond, so I think it should be rare, as coopted and coopting already are.
If there are no objections, I'll switch these to rare soon.
Thanks, everyone, for the suggestions.