See biography by B. Moin (2000).
The town was originally known as Sedeh. In the 1930s, the name was changed to Homayun-shahr. After the Iranian Revolution of 1979, the city was renamed again to Khomeini-shahr. Locals have continued to refer to the city as Sedeh.
It is commonly believed that the original name, Sedeh (Persian: سده), is derived from Seh-degh, meaning "three castle" in Persian, and is linked to formation of the formation of the town by the growth of three neighbouring castles The three main castles of kohan degh, gar degh, and .... degh (degh means castle (دژ)locally pronounced kohan degh, gar dar)
It is commonly believed that seh degh was sasanian kings foot soldier baseit is an old fire place (atash gah) based on top of the mountain close of khomeini shahr(sedeh) . The three main village of Khouzan, Foroushan (the origin of foroushan was Parishan(pari(angel)+ voshan(face))), and Varnosfaderan (locally pronounced Khizoon, Perishoon(Foroushon), Venesfohoon) remain identifiable parts of the city.
However, there are in fact 5 former villages forming identifiable parts of the town. This has led to arguments that the name may have some other derivation such as a link to the ancient Persian festival of Sadeh.
The change to Homayun-shahr, took place during the reign of Reza Shah Pahlavi. The name literally means "auspicious or august city", but Homayun was also a title of the Shah and so the name was seen as being linked with the Pahlavi dynasty. Thus, after the revolution of 1979 the city was renamed again, this time to be called after Ayatollah Khomeini, the founder of the revolution.