from The Century Dictionary.
- noun Nautical, a common block or deadeye connected to a ringbolt by a spiral or india-rubber spring. It is attached to the sheets, so as to give a certain amount of elasticity.
- noun In a vehicle, a piece of wood fixed on the axle as a support for the spring.
- noun In a car-truck, a distance-piece placed above or below an elliptic spring.
Sorry, no etymologies found.
Your spring-block for assisting a vessel in sailing cannot be tried here, because the Seine, being not more than about forty toises wide, and running swiftly, there is no such thing on it as a vessel with sails.