underdrift

Adjective

 * 1)  Having the gearing that turns the millstone beneath the floor.

Noun

 * 1) An underlying meaning that is not made explicit.

Usage notes
The term underdrift to describe the gearing that drives a millstone is only used when describing windmills. Water-driven mills (those using a waterwheel) are always driven from below, and so, in that context, the term is not needed to distinguish the mechanism from that of an overdrift mill.

Etymology
.

Noun

 * 1) understatement