late 14c., dilaten, "describe at length, speak at length," from Old French dilater and directly from Late Latin dilatare "make wider, enlarge," from dis- "apart" (see dis-) + lātus "broad, wide, widespread, extended" (see latitude). Meaning "expand, distend, spread out, enlarge in all directions" (transitive) is from early 15c.; intransitive sense of "spread out, expand, distend" also is from early 15c. A doublet of delay. Related: Dilated; dilating.
<a href="https://www.etymonline.com/word/dilated">Etymology of dilated by etymonline</a>
Harper, D. (n.d.). Etymology of dilated. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/dilated