Siridar-Governor as depicted in the Dune CCG
Siridar is a Galach term for "planetary".
The term was used to describe planetary fiefs during the time of the Faufreluches. It was also a prefix for Barons who were planetary governors (i.e., "Siridar Baron").
Etymology[]
It is possible that the Galach siridar, Fremen al-asiridar derive from the original Arabic as-sadar i.e. "voice" [of the Emperor], this usage presumably referring to the fact that the designated official speaks in the Emperor's name to stipulate what will happen. It could also come from Persian Sirdar/Sardar, signifying a military or political leader, and literally meaning "head holder".
Perhaps, the Galach term might also derive from English sidereal ("astral", "stellar", "of the star"), which itself originates in the Latin term sidus ("star"). In this context, it would refer to those who rule a star system.