What is in general, a framing in wood or iron which is intended to receive an upright shaft; specif., a block of wood, or a solid platform upon the keelson, supporting the heel of the mast called?

step — (Naut.) In general, a framing in wood or iron which is intended to receive an upright shaft; specif., a block of wood, or a solid platform upon the keelson, supporting the heel of the mast. (Webster's 1913.)