The Fingers’ Names in Japanese Originate from Size or Usage
In Japan, fingers’ names are called the following:
#1 The thumb is oyayubi (親指), the “parent finger”.
#2 The index finger is hitosashiyubi (人差し指), the “pointing finger”.
#3 The middle finger has the same meaning as in English, and is called nakayubi (中指).
#4 The ring finger is called, kusuriyubi (薬指), the “medicine finger”.
#5 The pinky is koyubi (小指), the “little finger”
#1 is the biggest, so it’s called the “parent” finger. In the past, the Japanese would hide their thumbs into their hands when seeing a hearse, to prevent the bad luck of losing a parent too.
#5 is the smallest, so it’s called the “little” finger.
#3 is in the middle, so it’s called the “middle” finger.
#2 is called the “pointing” finger since you use this finger to ‘point things out’ to other people. Pointing at people is usually considered bad manners.
#4, the term “medicine finger” is derived from the fact that doctors used to use this finger when they mixed medicine or applied ointment.
Fingers of the Hand as Family Members
In order to teach little children the names of the fingers, they are sometimes represented as a family! It’s cute and easy to remember for children:
The thumb is the “father finger”, otoosanyubi（お父さん指）.
The index finger is the “mother finger”, okaasanyubi（お母さん指）.
The middle finger is the “brother finger”, oniisanyubi （お兄さん指）.
The ring finger is the “sister finger”, oneesanyubi (お姉さん指)
And the pinky is the “baby finger”, akachanyubi (赤ちゃん指).