digityoudaoicibaDictYouDict[digit 词源字典]
digit: [15] Digit was borrowed from Latin digitus. This meant ‘finger or toe’, but its underlying etymological sense is probably ‘pointer’; it appears to come from an Indo-European base *deik-, which also produced Latin dicere ‘say’ (originally ‘point out’), Greek deiknúnai ‘show’, Sanskrit diç- ‘show’, and possibly English toe.

The word was used in classical times for a measure of length, a ‘finger’s breadth’, but the mathematical sense ‘any of the numbers from 0 to 9’ (originally as counted on the fingers) is a later development. Digitalis [17], the scientific name of the ‘foxglove’, is a modern Latin use of the Latin adjective digitālis ‘of the finger’, perhaps in allusion to the foxglove’s German name fingerhut ‘thimble’, literally ‘finger-hat’.
=> toe[digit etymology, digit origin, 英语词源]
digit (n.)youdaoicibaDictYouDict
late 14c., "numeral below 10," from Latin digitus "finger or toe" (also with secondary meanings dealing in counting and numerals), related to dicere "tell, say, point out" (see diction). Numerical sense is because numerals under 10 were counted on fingers. The "finger or toe" sense in English is attested from 1640s.