A finger (sometimes fingerbreadth or finger's breadth) is any of several units of measurement that are approximately the width of an adult human finger, including:
The digit, also known as digitus or digitus transversus (Latin), dactyl (Greek) or dactylus, or finger's breadth — 3⁄4 of an inch or 1⁄16 of a foot.
In medicine and related disciplines (anatomy, radiology, etc.) the fingerbreadth (literally the width of a finger) is an informal but widely used unit of measure.
In the measurement of distilled spirits, two fingers of whiskey refers to the amount of whiskey that would fill a glass to the level of two fingers wrapped around the glass at the bottom.
Another definition (from Noah Webster): "nearly an inch."
Finger is also the name of a longer unit of length used in cloth measurement, specifically, one eighth of a yard or 4 1⁄2 inches.
In English these units have mostly fallen out of use, apart from the common use in distilled drinks and drinking games.