It's derived from French "côtelette", literally "little rib". It's etymologically related to "coast", actually. It being spelled "cutlet" is probably the result

It's derived from French "côtelette", literally "little rib". It's etymologically related to "coast", actually. It being spelled "cutlet" is probably the result of a phonetic spelling of "côtelette" in English being reanalyzed as "cut-let", though, since "a cut of meat" is itself a thing. It originally referred to the same thing "chop" does today, a slice of meat perpendicular to the spine, containing a single rib. Then it started referring specifically to a boneless chop. Then it started being used to refer to any thin slice of meat. And in a lot of the world it was introduced specifically as a breaded and fried thin slice of meat. And that's how we got katsu, the Japanese version of schnitzel. Language is weird, isn't it?