Palm (unit)

The palm is an obsolete anthropic unit of length, originally based on the width of the human palm and then variously standardized. The same name is also used for a second, rather larger unit based on the length of the human hand.

The width of the palm was a traditional unit in Ancient Egypt, Israel, Greece, and Rome and in medieval England, where it was also known as the hand,handbreadth, or handsbreadth. The only commonly discussed "palm" in modern English is the biblical palm of ancient Israel.

The length of the hand—originally the Roman "greater palm"—formed the palm of medieval Italy and France.

The Spanish and Portuguese "palm" (palmo or palmo de craveira) was the span, the distance between an outstretched thumb and little finger.

The Ancient Egyptian palm (Egyptian: shesep) has been reconstructed as about 75 mm or 3 in. The unit is attested as early as the reign of Djer, third pharaoh of the First Dynasty, and appears on many surviving cubit-rods.

...
Wikipedia