To the shipwright a spline is a thin strip of wood which is glued into a seam when the gap is too wide for ordinary caulking. Similarly a spline may be used to repair a cracked plank, after the crack has been opened with the saw to make a slot of regular shape. On the drawing board, too, a spline is a thin strip of wood (sometimes of other flexible material) which can be used to draw curved lines such as hull waterlines. In the engineering shop a spline is a raised ridge on a shaft which keys into a corresponding slot on a pinion or other female member. As a verb, you would spline a crack in a hull, and you would have a splined shaft