Dip of the horizon
|(Astron.)||the angular depression of the seen or visible horizon below the true or natural horizon; the angle at the eye of an observer between a horizontal line and a tangent drawn from the eye to the surface of the ocean.|
|(Astron.)||the vertical angle between the sensible horizon and a line to the visible horizon, the latter always being below the former.|
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.