According to Adler, this puzzling entry is found also in the unpublished Lexicon codicis Barocciani 50 (ff.109-110). It does not appear to be a Latin word, unless perhaps it was an abbreviation of scriptura. It resembles the Arabic word sūra used for chapters of the Qur'an, for which etymologies in Hebrew and Syriac have been suggested (see Wikipedia entry at web address 1, and Jeffery p. 181-2).