I was surprised to find "shill" listed as a common word in the "shrillest" puzzle. I've never heard of it, and for me I think that's a first for words listed as common. Chambers online doesn't list it, and OED lists it, but classifies it as "slang (chiefly N. Amer.)" - which is probably why I, an Aussie, don't know it! Question is: if it's only common in one part of the world, is it appropriate to list it as common?