What is (a) To unfasten, as sails, from the spars or stays to which they are attached for use. (b) To cast loose or untie, as a rope called?

unbend — (Naut.) (a) To unfasten, as sails, from the spars or stays to which they are attached for use. (b) To cast loose or untie, as a rope. (Webster's 1913.)