I've gone papula as that's the option given first in the Concise OED that I use.
But, given that the answer given today to one of last week's linked clues was Errant Knight as opposed to Knight Errant, which we all thought was correct, who knows?
rhis is a very bad and misguided joke. there is no such thing as an errant knight (unless you count someone caught, say, in flagrante). errant knight is totally wrong.