U.K. vs billion

U.K. and billion both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.K.	Yes	No	No	No
billion	Yes	Yes	No	No

U.K. (noun)	billion (noun)
a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom	the number that is represented as a one followed by 9 zeros
	the number that is represented as a one followed by 12 zeros; in the United Kingdom the usage followed in the United States is frequently seen
	a very large indefinite number (usually hyperbole)

U.K. (adjective)	billion (adjective)
	denoting a quantity consisting of one thousand million items or units in the United States
	denoting a quantity consisting of one million million items or units in Great Britain