Short answers, pulled from the story.
The earliest known reference to the word Afghan appears in the 3rd century CE, carved into the rock inscriptions of Shapur I of the Sassanid Empire. This event marks the first time this ethnonym entered the historical record.
The linguistic root of the name Afghan is widely believed to derive from the Sanskrit word Asvaka, which translates directly to horsemen or cavalrymen. This etymology reflects the historical reality of the region, where the terrain and culture were inextricably linked to the breeding and handling of superior horses.
The coined term Afghanistan, referring to the land of the Afghans, came into official use in 1855, recognized by the British during the reign of Dost Mohammad Khan. This formalization of the state name was a political necessity that transformed the word from a specific reference to the Pashtun people into a broader demonym for all residents of the territory.
The 1612 text Maqzan-e Afghan by Nimat Allah al-Harawi traces the name to an eponymous ancestor named Afghana, identified as a grandson of the biblical King Saul. According to this narrative, Afghana was the son of Irmia, or Jeremia, and was orphaned at a young age before being raised by King David.
One hypothesis, advanced by H. W. Bellew in 1891, suggests that the name derives from the Latin term albus, meaning white, or mountain, as mountains are often white-capped with snow. This theory posits that the name was used by Armenians as Alvan or Aghwan to refer to mountaineers, and was later altered by Persians to Aoghan, Avghan, and finally Afghan as a reference to the eastern highlanders.