Eustace, also rendered Eustis, is the rendition in English of two phonetically similar Greek given names: Εὔσταχυς meaning "fruitful", "fecund"; literally "abundant in grain"; its Latin equivalents are Fæcundus/Fecundus Εὐστάθιος meaning "steadfast", "stable"; literally "possessing good stability"; its exact Latin equivalents are Constans and its derivatives, Constantius and Constantinus. Wikipedia