So why do we call the digits at the end of our limbs what we do? Let’s find out!
As a verb (like, to finger something) showed up in the early fifteenth century, and as a noun it showed up sometime before that, although there’s no specific date. It comes from the Old English finger, which means…finger. Shocking. As to where it came from before that, no one knows. It might be related to a Proto Indo European word for five, which makes sense since there are five of them (including the thumb) but that’s just a guess.
Thumb comes from the Old English Þuma—Þ is thorn, so the word is thuma, and of course it means thumb. It comes from the Proto Germanic thumon, which apparently meant “the stout finger”. Before that, it was the Proto Indo European tum-, swell. So because the thumb is the fattest of your hand digits, it’s related to swell.
Toe comes from the Old English ta, which of course means toe and is even cuter than the word toe. It’s actually a contraction of another word, tahe, which comes from the Proto Germanic taihwo. Because that word may have originally meant finger as well as toe, and if it is, it’s related to the Proto Indo European deik, to point out, and the origin word for digit.
Tony Jebson’s page on the Origins of Old English