Latin, meaning: even if, although. 
Tametsi (Latin, `although`) is the legislation of the Catholic Church which was in force from 1563 until Easter 1908 concerning clandestine marriage. It was named, as is customary in Latin Rite ecclesiastical documents, for the first word of the document that contained it, Chapter 1, Session 24 of the Council of Trent. This was the document that.....