What, if any, naming convention was used for the standard Unix commands?

I was trying to find the naming convention for Linux commands. For commands like cp, rm, mv, etc it seems to be based on first and second last character like * move is mv * list is ls * copy is cp * change directory is cd, the first character of two words, which makes sense while sometimes ignoring vowels in some commands, which makes sense. On the other hand, the command mkdir is not based on the previous perception: "make directory" is mkdir which should be more like md. As we have naming convention for a variable in a bash script and another guide line (for example 1 , 2 ), I am wondering whether any similar convention exists for these commands.