From the second edition (1989):
(snaɪ) [Cf. snying vbl. n.]
(See quots. 1846 and 1875.)
a. 1711 W. Sutherland Shipbuild. Assist. 54 In working up a round Buttock of a Ship, the lower Edge of the Planks will have a sudden Sny aft. 1846 A. Young Naut. Dict. 288 In shipbuilding, a plank is said to have sny, when its edge has an upward curve.
b. c1850 Rudim. Nav. (Weale) 149 The great sny occasioned in full bows‥is‥to be prevented by introducing steelers. 1875 Knight Dict. Mech. 2232/1 Sny,‥the trend of the lines of a ship upward from amidship toward the bow and the stern.