finger (n.) Look up finger at Dictionary.com
"terminal or digital member of the hand" (in a restricted sense not including the thumb), Old English finger, fingor "finger," from Proto-Germanic *fingraz (cognates: Old Saxon fingar, Old Frisian finger, Old Norse fingr, Dutch vinger, German Finger, Gothic figgrs "finger"), with no cognates outside Germanic; perhaps connected with PIE *penkwe-, the root meaning "five."

As a unit of measure for liquor and gunshot (late Old English) it represents the breadth of a finger, about three-quarters of an inch. They generally are numbered from the thumb outward, and named index finger, fool's finger, leech- or physic-finger, and ear-finger.
finger (v.) Look up finger at Dictionary.com
early 15c., "to touch or point to with the finger" (but see fingering (n.1) from late 14c.), from finger (n.). Sense of "play upon a musical instrument" is from 1510s. Meaning "touch or take thievishly" is from 1520s. The meaning "identify a criminal" is underworld slang first recorded 1930. Related: Fingered; fingering. Compare Dutch vingeren, German fingern, Swedish fingra, all from their respective nouns.