Fr. On; upon; over. In the titiles of real actions “sur’’ was used to point out what the writ was founded upon. Thus, a real action brought by the owner of a reversion or seigniory, in certain cases where his tenant repudiated his tenure, was called “a writ of right sur disclaimer.” So, a writ. of entry sur disseisin was a real action to recover the possession of land from a disseisor. Sweet.