A male name. there are two saints named Eustachius in the Roman Calendar, one of them having the same day as St Eustathius in the Greek Calendar, and the two names are often supposed to be identical. But there is no trace of confusion between them at an early period, and though Eustachius is not easy to explain etymologically, that is no reason for confounding it with Eustathius (from Greek εύστάθης 'tranquil’, ‘stable’). It may possibly be from εύσταχυς ‘fruitful’. The better known of the two saints Eustachius was a 2nd- C Roman soldier, whose legend included the story of his conversion, while hunting, by the vision of a crucifix between the horns of a stag. He was, like St Hubert, a patron saint of huntsmen. His relics were transferred at an early date to St Denis, and Eustache was a common French name. It was brought to England by the Normans and was fairly common in the 12th and 13th C. In Latin it appears as Eustachius or Eustacius, in English as Eustace, Eustas or Ewstace, and gave rise to the surnames Eustace, Eustes, Eustis. It has continued in infrequent use till the present day.

Eustacius, Eustachius Regesta Regum Anglo-Normannorum 1076-84, Domesday Book 1086, Curia Regis Rolls 1196-1215, Feudal Aids 1303, 1316. Eustace, Ewstace Hundred Rolls 1273.