The word 'digit' entered English in the fifteenth century from Latin 'digitus,' meaning 'finger' or 'toe.' The mathematical sense — any of the numerals from 0 to 9 — developed because humans count on their fingers, and the ten fingers of the hands naturally correspond to the ten symbols of the decimal (base-10) number system. The word thus preserves one of the most fundamental connections in human culture: the link between the body and mathematics, between fingers and numbers.
The Latin word 'digitus' may derive from Proto-Indo-European *deyḱ- (to show, to point out), the same root that produced Latin 'dicere' (to say, to point out — source of English 'diction,' 'dictate,' 'dictionary'), Latin 'index' (one who points out — from 'indicāre,' to point to), and Greek 'deiknýnai' (to show). If this etymology is correct, the finger was named as 'the pointer' — the body part that shows and indicates. This derivation is debated among linguists, but the semantic fit is compelling: the finger's primary communicative function is to point.
The connection between fingers and counting is universal. Virtually every human culture uses the fingers for counting, and the dominance of base-10 number systems worldwide reflects the biological fact that humans have ten fingers. (The vigesimal base-20 systems found in some languages — Mayan, Basque, traces in French — may reflect counting on both fingers and toes.) The word 'digit' makes this connection explicit: a digit is both a finger and a number, and the two senses are not metaphorically related but causally connected — we have ten numerical digits because we have ten anatomical digits.
In Roman measurement, a 'digitus' was also a unit of length — approximately three-quarters of an inch (about 19mm), the width of a finger. This unit appeared in architectural specifications, engineering calculations, and astronomical measurements. The finger-width as a measuring unit is attested across many ancient cultures: the Egyptian 'djeba,' the Greek 'dáktylos,' and the Sanskrit 'aṅgula' all named a finger-width measurement, suggesting that the practice of measuring with fingers is as old as measurement itself.
The mathematical sense of 'digit' — a single symbol in a numeral system — became firmly established in English during the seventeenth century and expanded in the twentieth century with the rise of computing. 'Digital' — literally 'of or pertaining to fingers' — acquired its modern technological meaning in the 1940s and 1950s, when engineers needed a word to describe computers that processed information as discrete numerical values (digits), as opposed to 'analog' computers that processed continuously variable physical quantities. The 'digital' in 'digital computer' thus means 'operating with digits' — with discrete numerical symbols — and the entire digital revolution is named, at two removes, after the human finger.
The transition from 'digital' meaning 'of fingers' to 'digital' meaning 'of electronic technology' is one of the most dramatic semantic shifts of the twentieth century. A 'digital watch' does not use fingers; a 'digital photograph' has nothing to do with hands; 'digital literacy' does not involve finger dexterity. Yet in each case, the connection to the Latin 'digitus' is traceable: the technology processes digits (numbers), which are named after fingers (the original counting tools). The chain is finger → number → electronic processing of numbers.
The botanical and medical word 'digitalis' — the genus name of the foxglove plant, used to treat heart conditions — also derives from Latin 'digitus.' The plant was named 'digitalis' by the German botanist Leonhart Fuchs in 1542 because its flowers resemble thimbles or finger-coverings. The cardiac drug digitalis, extracted from foxglove and used to treat arrhythmias since the eighteenth century, thus shares its name's origin with digital computers — both named for the shape and function of the human finger.
The word 'prestidigitation' — sleight of hand, conjuring tricks — combines Latin 'praesto' (ready, at hand) with 'digitus' (finger) to mean, roughly, 'ready-fingered' or 'nimble-fingered.' The word acknowledges that the magician's art depends on the agility and dexterity of the fingers — the digits that give the word 'dexterity' itself (from Latin 'dexter,' the right hand).
Across European languages, the Latin root produced the standard words for 'finger': French 'doigt' (from 'digitus' through regular sound changes), Spanish 'dedo,' Italian 'dito,' Portuguese 'dedo,' Romanian 'deget.' The mathematical sense — digit as numeral — is carried by some of these: Spanish 'dígito' (numeral), Italian 'digit' or 'cifra,' French 'chiffre.' German diverges, using 'Finger' (from Germanic) for the body part and 'Ziffer' (from Arabic 'ṣifr,' through Latin 'cifra') for the numeral — keeping the anatomical and mathematical senses in separate etymological families that English 'digit' uniquely unites.