word-forming element in modern use meaning "good, well," from comb. form of Greek eus "good," eu "well" (adv.), also "luckily, happily," from PIE *(e)su- "good" (cf. Sanskrit su- "good," Avestan hu- "good").
eu- pref.
Good; well; true: eupepsia.
A derivative of a specified substance: euglobulin.