The English word
PAJAMAS comes to us from Urdu
pajama, which is in turn from Persian
pay-
jamah, leg-clothing. The spelling "pajamas" is more common in the United States, while the spelling "pyjamas" is the common British spelling. You can read more about the history and variety of pajamas in this
Wikipedia article.
In my family, they were always just called PJs or jammies. I've also heard them called jimjams!
Here's a cute picture of girls in their pajamas (by
cobalt123 at Flickr... aka
BJ Bolender):