either of a pair of torpedo-shaped devices which, in conjunction with the cables by which they are towed from the bow of a ship, are used to cut the moorings of submerged mines, allowing them to surface and be destroyed
para- + vane
See paravane in American Heritage Dictionary 4
A device equipped with sharp teeth and towed alongside a ship to cut the mooring cables of submerged mines.
Origin: From its having vanes to keep it at a constant depth