expansion vs dilation

expansion and dilation both are nouns.

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

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

expansion: the act of increasing (something) in size or volume or quantity or scope
dilation: the act of expanding an aperture

Other hyponyms of expansion include dilatation, distension, distention, stretching, inflation, magnification, extension.

expansion (noun)	dilation (noun)
the act of increasing (something) in size or volume or quantity or scope	the act of expanding an aperture
adding information or detail	a lengthy discussion (spoken or written) on a particular topic
a discussion that provides additional information
a function expressed as a sum or product of terms