"Xenopus laevis" is the scientific name for the African clawed frog
Xenon is a chemical element. It begins with the letter x.
A good scientific term beginning with x is x-ray.
Xenon is chemical element #54. It begins with the letter X.
Xavior.
xena
X-zibit
xanadu.
Xavier
As of 2014, no nation's name starts with X.
The scientific name for boysenberries is Rubus ursinus x idaeus.
No country's English name begins with an X, but perhaps that is not your question.... * Luxembourg and * Mexico .... both have an X in their name.