xenon
X-ray
Xavier
xanadu
A noun referring to "one who is xenophobic" is a xenophobe.
There is no widely recognized collective noun that starts with "x." However, you could perhaps use "xenolith" to refer to a group of geologically associated foreign rock inclusions. Keep in mind that this term is specific to the field of geology.
An "island" is a common noun that starts with the letter "i."
Abstract nouns that start with X, Y, or Z are:xylographyyearyesterdayyieldyouthzealzealousnesszoologyzymurgy
Wikipédia is a French noun that starts with w.
The noun yellow starts with y- and ends with -w.
A nine letter abstract noun that starts with U is ultimatum.
The collective noun for soldiers that starts with S is squad.
no tree starts with x