extension vs spreading

extension and spreading both are nouns.

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

As nouns, spreading is a hyponym of extension; that is, spreading is a word with a more specific, narrower meaning than extension:

Other hyponyms of extension include spread, stretch.

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

extension: the spreading of something (a belief or practice) into new regions
spreading: the opening of a subject to widespread discussion and debate

Other hypernyms of extension include airing, dissemination, public exposure.

extension (noun)	spreading (noun)
an educational opportunity provided by colleges and universities to people who are not enrolled as regular students	act of extending over a wider scope or expanse of space or time
act of stretching or straightening out a flexed limb	the opening of a subject to widespread discussion and debate
act of expanding in scope; making more widely available	process or result of distributing or extending over a wide expanse of space
an addition that extends a main 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