extension vs building

extension and building both are nouns.

Word	Noun	Adjective	Verb	Adverb
extension	Yes	No	No	No
building	Yes	No	No	No

extension (noun)	building (noun)
an educational opportunity provided by colleges and universities to people who are not enrolled as regular students	the act of constructing something
act of stretching or straightening out a flexed limb	the commercial activity involved in repairing old structures or constructing new ones
act of expanding in scope; making more widely available	a structure that has a roof and walls and stands more or less permanently in one place
an addition that extends a main building	the occupants of a building
an addition to the length of something
an additional telephone set that is connected to the same telephone line
amount or degree or range to which something extends
the ability to raise the working leg high in the air
the most direct or specific meaning of a word or expression; the class of objects that an expression refers to
a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename
the spreading of something (a belief or practice) into new regions
a mutually agreed delay in the date set for the completion of a job or payment of a debt