Spill—To throw the wind out of a sail by putting the helm down or by easing the sheet.
Spring—To spring a spar is to crack it.
Spring—A rope used to cast or turn a vessel.
Stand on—To keep a course—to proceed in the same direction.
Stand-by—To be ready for action, as stand-by to let go the anchor.
Starboard—The right-hand side looking forward. Designating color, green.
Steer—To direct a vessel by employing the helm.
Stow—To furl. Properly speaking, a boom sail or any sail that lowers down is stowed. Square sails are furled.
Swig—To haul a rope by holding a turn round a cleat and pulling off laterally.
Tack—To beat to windward. See diagram.