Autocannons are not machine guns

Chuck, you wouldn't list "short for goat's milk" as a definition for the word "milk". You could, on the other hand, list "milk that comes from a goat" as a definition for "goat's milk". So, you could go to "desktop personal computer" (if it was one word) and add a definition that it's a certain type of computer, but you wouldn't list desktop personal computer as a definition of computer.