Simplify the following text for a Grade 11 native English-speaking person.
Original: The derivation is probably from the Byzantine Greek word souda , meaning `` fortress '' or `` stronghold , '' with the alternate name , Suidas , stemming from an error made by Eustathius , who mistook the title for the proper name of the author .
Simplified: The derivation is probably from the Byzantine Greek word souda , meaning ` fortress ' or ` stronghold ' .