extension vs addition

extension and addition both are nouns.

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

As nouns, addition is a hypernym of extension; that is, addition is a word with a broader meaning than extension:

Other hypernyms of extension include add-on, improver.

As nouns, addition is a hypernym of extension; that is, addition is a word with a broader meaning than extension:

Other hypernyms of extension include add-on, improver.

extension (noun)	addition (noun)
an educational opportunity provided by colleges and universities to people who are not enrolled as regular students	the arithmetic operation of summing; calculating the sum of two or more numbers
act of stretching or straightening out a flexed limb	the act of adding one thing to another
act of expanding in scope; making more widely available	a component that is added to something to improve it
an addition that extends a main building	a suburban area laid out in streets and lots for a future residential area
an addition to the length of something	something added to what you already have
an additional telephone set that is connected to the same telephone line	a quantity that is added
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