I’ve long puzzled about why the ring finger is called third finger in spite of it being the forth finger from the thumb (counting the thumb as the first, the pointing finger the second, the middle finger as the third) and the second from the little finger.
Wikipedia describes it as;
the fourth proximal digit of the human hand, and the second most ulnar finger, located between the middle finger and the little finger. It is also called digitus medicinalis, the fourth finger, digitus annularis, digitus quartus, or digitus IV in anatomy. In Chinese it’s called 无名指 - unnamed finger.
Nothing is related with “the third.”
We Japanese also call the ring finger "薬指- kusuri-yubi" meaning the finger (only) used for tasting and examining medicine.
How did the ring finger come to be called the third finger?
For your refference;
Cambridge online English Dictionary defines finger as “One of the five long parts at the end of your hand.”
Oxford online English Dictionary defines finger as “Each of the four slender jointed parts attached to either hand, or five, if the thumb is included.
Merriam-Webster English Dictionary defines finger as “One of the five long parts of the hand that are used for holding things; especially: one of the four that are not the thumb.”