We all know Japanese people work hard, study hard and do even party hard and there are a few words in the language that show it. Some of which I already talked about in the past. This one is a nice one, pointing at the "study hard" category. I was asked if this word exist in English and couldn't quite tell, I have never heard of it but I'm not a native English speaker.
Anyway, the word is:
Reading: pen dako
Meaning: the callus one develops on one middle finger after writing A LOT.
Literally: pen callus
I also developed this pen callus sometimes when I was in school, but not enough times to actually have the need to invent a word for it.
There is a similar word, that refers to the traditional Japanese sitting habits.
Reading: suwari dako
Meaning: calluses (on one's ankles, insteps, etc.) caused by sitting seiza
Literally: sitting callus
I don't have those sitting calluses, since I can't even sit seiza for more than a minute :P
And it has been long since I actually used a pencil/pen, so my fingers are callus-free!