Riddle Fun: Solved!

So what is this mystery word?

If you haven't had a chance to read the riddle yet, here it is again:
There's a word in the English language which ends in "s" and is masculine plural.  When you add an "s," it turns into feminine singular.  What is it?
And now for a hint--

These are mine.

Do you have it yet?

It's:

Princes and Princess

Neato, huh?

I thought so.

Thanks to Lynn (who inspired the idea for this post and correctly answered via text), Missy, and Jocelyn for playing along and answering correctly!

Guess, what?  You each have won a prize!

Lynn gets unlimited babysitting, whenever mutually agreeable.  (Oh, wait, she already has that.)

Jocelyn gets on-the-spot-at-our-home care for her family if she and her husband ever happen to be struck with food poisoning while visiting us.  (Well, she already got that back in December of 2008.)

And Missy gets two mornings of free childcare for her two or three sweet little girls(she chooses whether or not to share her brand new peanut with me), whenever we can mutually agree upon some dates. (And that is actually a prize!  For serious!)

So congratulations, ladies!  And thanks for being faithful readers, commenters, and, most importantly, in-real-life friends.

See what happens when you play along here at Tulipa Murillo?  You may even win something!  (And don't remind me about those cookies for my 200th post.  I'm such a loser.  Obviously, I need to give away mostly prizes that I've previously given to the winners.  It's the ultimate in re-gifting, I suppose.)