What is Ancipitis Usus?

Legal Definition
Lat. In international law. Of doubtful use; the use of whieh is doubtful; that may be used for a civil or peaceful, as well as military or warlike, purpose. Gro. de Jure B. lib. 3, c. 1, § 5, subd. 8; 1 Kent, Comm. 140.
-- Black's Law Dictionary
Legal Definition
Of uncertain use.
-- Ballentine's Law Dictionary