English word iso- comes from Ancient Greek ἴσος

Detailed word origin of iso-

Dictionary entry	Language	Definition
ἴσος	Ancient Greek (grc)
iso-	English (eng)	(chemistry) forms terms relating to isomers. (mathematics) forms terms relating to isomorphisms. (organic chemistry) (of an aliphatic compound, especially a fatty acid) Having a branch on the penultimate carbon atom of a chain. (physics) forms terms relating to isotopes. Equal.