distention vs expansion

distention and expansion both are nouns.

Word	Noun	Adjective	Verb	Adverb
distention	Yes	No	No	No
expansion	Yes	No	No	No

As nouns, expansion is a hypernym of distention; that is, expansion is a word with a broader meaning than distention:

distention: the act of expanding by pressure from within
expansion: the act of increasing (something) in size or volume or quantity or scope

Other hypernyms of distention include enlargement.

distention (noun)	expansion (noun)
the act of expanding by pressure from within	the act of increasing (something) in size or volume or quantity or scope
the state of being stretched beyond normal dimensions	adding information or detail
	a discussion that provides additional information
	a function expressed as a sum or product of terms