Fox, box, tax, sax
xylophone, xerox, x-ray
Examples of common nouns ending in X:axboxcrucifixcruxduplexequinoxflaxfoxhexibexindexjinxlarynxloxlynxmatrixminxmixonyxoryxoxparadoxphoenixphloxpoxprefixrouxsexsixsmallpoxspandexsuffixsyntaxtaxthoraxvortexwax
Abstract nouns that start with X, Y, or Z are:xylographyyearyesterdayyieldyouthzealzealousnesszoologyzymurgy
The word 'World X' is a proper noun, the name of a company, World X Productions, LLC. A proper noun is the name of a person, place, thing, or a title. A proper noun is always capitalized. However, the word is a common noun when not referring to the above company. For example, 'When world X conflicts with world Y, a science fiction tale is born.' This use of 'world x' is a common noun.
Trans-X ended in 1986.
Special X ended in 2008.
X Club ended in 1893.
Liberty X ended in 2007.
Bre-X ended in 2003.
Spirea X ended in 1993.
X-Wild ended in 1997.
X-Sinner ended in 2001.