Why does ENOENT mean "No such file or directory"?
Solution 1:
It's an abbreviation of Error NO ENTry (or Error NO ENTity), and can actually be used for more than files/directories.
It's abbreviated because C compilers at the dawn of time didn't support more than 8 characters in symbols.
Solution 2:
It's simply “No such directory entry”. Since directory entries can be directories or files (or symlinks, or sockets, or pipes, or devices), the name ENOFILE would have been too narrow in its meaning.