n A rectangular piece that fits grooves like key seats in a hub and a shaft, so that while the one may slide endwise on the other, both must revolve together.
n A flexible strip of metal or other material, that may be bent into a curve and used in a similar manner to a ruler to draw smooth curves between points.
n (mathematics|computing) Any of a number of smoothcurves used to join points.
n (context|woodworking) A strip of wood or other material inserted into grooves in each of two pieces of wood to provide additional surface for gluing.
v (mathematics|computing) To smooth (a curve or surface) by means of a spline.