Definition of girdle

i. A thin sandstone stratum.

Ref: Standard, 2

ii. Flattened lenticles or nodules of any hard stone in softer beds. Sometimes extended also to beds.

Ref: Arkell

iii. In stratigraphy: (1) a thin stratum, particularly said of sandstone or coal, esp. when exposed in a shaft or borehole or (2) flattened lenticles or nodules of any hard stone in softer beds.

iv. In gemology, the line that encompasses a cut gem parallel to the horizon; or that determines the greatest horizontal expansion of the stone.

v. In structural petrology, on an equal-area projection, a belt or concentration of points representing orientations of fabric elements. If this belt coincides approx. with a great circle of the projection, it is referred to as a great-circle girdle. If the belt of concentration coincides approx. with a small circle of the projection, it is called a small-circle or 'cleft girdle'