Hello, KeebTalk.
Initially I wanted to post this question to r/mk but … maybe this etymologic, historic, and scientific question better fits KeebTalk (and is a great reason to finally join this board).
The question is simple, why is it called “Tenkeyless” … or, going back one step further, why is the numeric keypad called “ten key”?
Never have I ever seen a numeric keypad or some calculator with ten keys only, so I’m really excited on where this name comes from.
Thank you very much!
Here is a good explanation 
https://keyboard.university/100-courses/keyboard-sizes-layouts
EDIT: At least you asking for deeper meaning, then my answer obviously is a fail haha
I believe “tenkey” is actually a rare case of a Japanese-created English word that has been reimported back into English. Obviously it refers to the numbers from one to ten, but it has always seemed like an odd term to me, and its origins in Japanese are probably the reason why. (For what it’s worth I am a Japanese translator and a number of my dictionaries mark the term as wasei-eigo, or Japanese-created English.)
The accountant where I used to work called it a “tenkey” pad as well - I’m guessing 1-9 plus 0 being ten character keys?
Interesting question that started me searching around as I used to be really interested in collecting old calculators: the only one I ever bought though was a Burroughs Class 3 for $5 at a garage sale. Anyway. An article on wikipedia lead me to this (What is a Ten Key? (with pictures)) which describes “ten key” as the configuration of three rows of numbers 1-9 first used in 1911 on a Sundstrand Adding Machine. If you google that for images you’ll see that it had more than those 9 keys, but those are in prominent white. The article goes on into more detail about the whole world of ten key typing that I had no idea about.
As far as I’ve known; numpads have been called a tenkey or “ten key” for quite a while (that part of history I haven’t researched on); hence a keyboard without a numpad is tenkeyless.
Yeah … would be interesting, where the term “tenkey” or “ten key” comes from. If the word English word is derived from some Japanese wasei-eigo, that would even be more interesting.
There’s ten keys for 0–9, sure … but I’m not aware those ten keys have alway been on their own, without any modifiers or e.g. the decimal point.