What is Bilinguis?

Legal Definition
English law. One who uses two tongues or languages. Formerly a jury, part Englishmen and part foreigners, to give a verdict between an Englishman and a foreigner. Vide Medietas Linguae, Plowd. 2. It is abolished in Pennsylvania. Act April 14, 1834, §149.
-- Bouviers Law Dictionary
Legal Definition
Of a double language or tongue; that can speak two languages. A term applied in the old books to a jury composed partly of Englishmen and partly of foreigners, which, by the English law, an alien party to a suit is, in certain cases, entitled to ; more commonly called a "jury de medietate linguoe." 3 Bl. Comm. 360; 4 Steph. Comm. 422.
-- Black's Law Dictionary
Legal Definition
Speaking two languages.
-- Ballentine's Law Dictionary