Word Puzzle

While we were in Canada, we were listening to Click and Clack, the car guys, on CBC radio (July 6th, to be exact). They put out the following puzzle:

Most English words form their plural by adding "s" to the singular, so, most or all of the letters of the singular form of the word are in the plural form. In The Lord of the Rings, there's a plural word used which is the plural of a VERY common English word, yet has not one letter in common with the singular form. Can you guess (or do you know) what it is?

Answer is here in the magic of "inviso text" (aka, white on white* - highlight with your mouse to view it:  singular = cow; plural = kine. Hey, don't gripe - nobody said it was a plural form that got a lot of use these days!

*or actually, green on green - d'oh. Sorry.