Complex sentence: It is an occupation name, literally meaning "control" (sī) "horses" (mǎ), similar to the common English surname Marshall, which is derived from the Frankish: "mare" (horse) + "skalkoz" (master).
Split into simpler sentences: It is an occupation name, literally meaning "control" (sī) "horses" (mǎ). Coincidentally, this name has almost the same meaning as the common English surname Marshall, which is derived from the Frankish: "mare" (horse) + "skalkoz" (master).