How do I change a keyword from plural to singular?

Question

Ex: I have windmill and windmills as keywords.  I want them all to be windmill.  It won't let me change windmills to windmill because it says it already exists.  If I delete it, it deletes it from all the images that use the plural keyword. 

Answer 1

Sort of.....the number in the Keyword List shows the correct number of files with that particular keyword, clicking on that should populate the grid with those files. But stacking can be a confusion....if there's a closed stack or two with that keyword, all you see in the grid are the images at the top of the stack plus those not in a stack. In that event the library filter above matches the number of thumbnails showing in the grid, which will be lower that the actual number in the keyword list.
A bigger confusion is if there's a closed stack with the top image NOT having that keyword, but one or more images in the stack do have that keyword. In that situation, the stack is simply not displayed at all when clicking on the arrow to the right of the keyword in the keyword list.
Obvious solution is to expand all stacks, but that has to be done with filters off, as doing it while in a filtered search seems to have no effect.