OMBRE. A fish, more commonly called grayling, or umber.
ON. The sea is said to be "on" when boisterous; as, there is a high sea on.
ON A BOWLINE. Close to the wind, when the sail will not stand without hauling the bowlines.
ONAGER. An offensive weapon of the middle ages.
ON A WIND. Synonymous with on a bowline.
ON BOARD. Within a ship; the same as aboard.
ONCIA. A gold coin of Sicily; value three ducats, or 10s. 10d. sterling.
ONCIN. An offensive weapon of mediæval times, consisting of a staff with a hooked iron head.
ON DECK THERE! The cry to call attention from aloft or below.
ONE-AND-ALL. A mutinous sea-cry used in the Dutch wars. Also, a rallying call to put the whole collective force on together.