expansion vs dilatation

expansion and dilatation both are nouns.

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

As nouns, dilatation is a hyponym of expansion; that is, dilatation 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
dilatation: the act of expanding an aperture

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

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