Kapiśa is related to and includes Kafiristan. The scholarly community holds that Kapiśa is equivalent to the Sanskrit Kamboja. Kamboja and Kapiśa are believed to be two attempts to render the same foreign word (which could not appropriately be transliterated into Sanskrit). Dr. S. Levi holds that Persian Kambujiya or Kau(n)bojiya, Sanskrit Kamboja as well as Kapiśa, all etymologically refer to the same foreign word. The evidence from third century Buddhist tantra text Mahamayuri, which uses Kabusha for Kapisha, and the Ramayana-manjri by Sanskrit Acharya, Kshmendra of Kashmir (11th century), which specifically equates Kapiśa with Kamboja, thus substituting the former with the latter, sufficiently attest that Kapiśa and Kamboja are the same. According to the Indian history series: History and Culture of Indian People, Kapisa and Kamboja are the same. Scholars such as Dr. Moti Chandra and Dr. Krishna Chandra Mishra also write that the Karpasika (of Mahabharata) and Kapisa (Ki-pin/Ka-pin/Chi-pin of the Chinese writings) are synonymous terms. Both Karpasika and Kapiśa are essentially equivalent to Sanskrit Kamboja. The Paninian term Kapiśi is believed to have been the capital of ancient Kamboja. Kapiśa (Ki-pin, Ke-pin, Ka-pin, Chi-pin of the Chinese records) refers to the Kamboja kingdom, located on the south-eastern side of the Hindukush in the Paropamisadae region. It was anciently inhabited by the Aśvakayana (Greek: Assakenoi), and the Aśvayana (Greek Aspasio) (q.v.) sub-tribes of the Kambojas. Epic Mahabharata refers to two Kamboja settlements: one called Kamboja, adjacent to the Daradas (of Gilgit), extending from Kafiristan to south-east Kashmir including Rajauri/Poonch districts, while the original Kamboja, known as Parama Kamboja, was located north of Hindukush in Transoxiana territory, mainly in Badakshan and Pamirs/Allai valley, as neighbors to the Rishikas in the Scythian land. Ptolemy refers to two Kamboja territories/and or ethnics - viz.: Tambyzoi, located north of Hindukush on Oxus in Bactria/Badakshan, and Ambautai, located on the southern side of Hindukush in Paropamisadae. The Komoi clan of Ptolemy, inhabiting towards Sogdiana mountainous regions north of Bactria, is believed by scholars to represent the Kamboja people. Front ranking scholars like Dr. S. Levi, Dr Michael Witzel, and numerous others accept the identity of Tambyzoi and Ambautai with Sanskrit Kamboja. The Ptolemian Ambautai formed parts of the Kapiśa kingdom under sway of Aśvakayana/Aśvayana (Aśvaka) Kambojas. It appears probable that the original home of the Kambojas was trans-Oxian Kamboja, from where some tribal sections moved southwards and established colonies in Paropamisan on southern side of Hindukush. Over time, the Paropamisan settlements came to be addressed as Kamboja proper, whereas the original Kamboja settlement lying north of Hindukush in Transoxiana became known as 'Parama-Kamboja', or furthest Kamboja. Some scholars call Parama Kamboja 'Uttara-Kamboja', or northern Kamboja or Distant Kamboja. The Kapisa-Kamboja equivalence, as suggested by scholars such as Dr. Levi, applies to the Paropamisan Kamboja settlement.
Kafir and Kafiristan etymologically derived from Kapiśa
According to the conventional etymology, the name "Kafir" derives from Arabic Kafir, commonly translated into English as "infidels" or "idolaters." Kafiristan, then, would be "The Land of the Infidels". This explanation would justify the renaming of the country after its Islamization.
Many historians, however, opine that the local name "Kafir" comes from Kapiś (= Kapish), the ancient Sanskrit name of the region that included historic Kafiristan. This is also given as "Ki-pin" (or Ke-pin, Ka-pin, Chi-pin) in old Chinese chronicles. This name, unrelated to the Arabic word, is believed to have, at some point, changed into the word Kapir. This linguistic phenomenon is not unusual for this region. The name of King Kanishaka, who once ruled over this region, is also found written as "Kanerika", an example of "ś" or "sh" changing to "r." In a similar way, Kapiś – the name of the people of Kapiś/Kapiśa – is believed to have changed to Kapir and then Kafir. One of the dominant clan of the Kafirs was known as Katir until recently.
The second change from Kapir to Kafir may have occurred spontaneously, since the exchange of "p" by "f" is common in Indo-European languages. It may also have been the result of confusion or intentional wordplay with the Arabic word, since the Kafirs were pagans until 1895.
The derivation of Kafiristan is now fairly easy, since -stan in Iranian language means country, abode, or place. Kafiristan would literally mean the land or abode of the Kafir (Kapir) peoples i.e. people belonging to Kapiśa.
Today, it is disputed if the term Kafir really defines a traditional ethnic group.