spreading vs extension

spreading and extension both are nouns.

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

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

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

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

Other hyponyms of spreading include circulation, propagation.

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