Delius, a, um, Idem. *Delius natator, Was one perfite in swimming. Whereof came a prouerbe, that when a thing was spoken or written, harde to be vnderstand, and required a cuuning exposito they would say, Delio natatore egit, it requireth a cunning or subtill expositor.
Lewis and Short: Latin dictionary
Dēlĭum, ĭi, n., *dh/lion, a small place in Boeotia, with a temple of Apollo, Cic. Div. 1, 54, 123; Liv. 35, 50 sq.