This word has been queried in the past, Tom. In one thread, Alan pointed out its commonality with other words and asked for comments. Maybe he did nothing about them because no one commented!
... there are a few other cases like axes. These ones at least, and perhaps some other more obscure words:
analysis / analyse / analyses
basis / base / bases
diagnosis / diagnose / diagnoses
ellipsis / ellipse / ellipses
marquis / marquise / marquises
paralysis / paralyse / paralyses
In fact, axes has two singular forms that would allow the word: ax and axis.
All of these plurals are currently disallowed. The issue may have never come up for most of them, but the letters for bases would probably have been available in several puzzles. Any comments?
