digitus.

Traditionally derived from Proto-Italic *digitos, from Proto-Indo-European *deyǵ- (“to show, point out, pronounce solemnly”), variant of the root *deyḱ- that also gave Latin dīcō (“to say, speak talk”) and English toe; fingers were thus "pointers" or "indicators". De Vaan, however, is skeptical, as no other term exhibits a comparable change from *-ḱ- to a *-ǵ-. The "number" sense comes from the fact that fingers were used for counting up to ten. Indo-European cognates include Sanskrit दिशति (diśáti, “to show, point out”), Ancient Greek δείκνῡμῐ (deíknūmĭ, “to show”), δῐ́κη (dĭ́kē, “manner, custom”), Old English tǣċan (“to show; to point out”, English teach) and tācn (“sign; token”, English token); compare the similar semantic shift in English teacher (“forefinger, index finger”). The relation to Ancient Greek δᾰ́κτῠλος (dắktŭlos, “finger”) is unclear, particularly as the latter term's phonetics suggest a substrate origin.