The difference between Buttock line and Waterline

Buttock line as a noun (aviation, ship-building):

A curve indicating the shape of an airfoil or nautical equivalent in a vertical plane parallel to the longitudinal axis of the craft or vessel.

Waterline as a noun (nautical):

A line formed by the surface of the water on the hull of a ship when she is afloat; any of a series of short lines marked on the hull to show where the waterline would be under different loadings.

Waterline as a noun (aviation):

A horizontal line indicating the shape of an airfoil.

Waterline as a noun:

A line showing where the water has been, usually a line separating dry land and wet areas; a watermark or tidemark.

Waterline as a noun (cosmetics):

the inner rim of the eyelid, just behind the lash line; primarily used in reference to the application of eyeliner.