Origins
The English word 'Persian' descends through Latin 'Persianus' and Greek 'Persis' (Περσίς) from Old Persian 'Pārsa,' the name of the southwestern Iranian province that served as the heartland of the Achaemenid Empire. In the cuneiform inscriptions of Darius the Great at Behistun (c. 520 BCE), 'Pārsa' designates both the homeland region and the people who ruled the largest empire the world had yet seen, stretching from Libya to the Indus. The Greeks adopted the name as 'Persis' and 'Persai' (the Persians), and it was through Greek — particularly the histories of Herodotus and Xenophon — that the name entered the European consciousness.
The ultimate origin of 'Pārsa' is uncertain. Some scholars have connected it to an Indo-Iranian root meaning 'edge,' 'border,' or 'side,' which would make Pārsa 'the borderland' — appropriate for a province on the edge of the Iranian plateau overlooking the Persian Gulf. Others have proposed a connection to a word for 'horse' or 'horseman,' reflecting the Persians' reputation as mounted warriors, but this remains speculative.
The transformation of 'Pārsa' into 'Fārs' is one of the most consequential sound changes in Middle Eastern linguistic history. When Arab armies conquered the Sasanian Persian Empire in the seventh century CE, Arabic phonology could not accommodate the /p/ sound, which does not exist as a native phoneme in Arabic. Every /p/ in borrowed Persian words was replaced by /f/: thus 'Pārsa' became 'Fārs,' and the adjective 'Pārsī' became 'Fārsī' (فارسی). When the Persian language reemerged as a literary medium in the ninth and tenth centuries — now written in Arabic script and heavily enriched with Arabic vocabulary — it adopted the Arabicized form of its own name. This is why the language is 'Persian' in English (preserving the Greek/Latin /p/) but 'Fārsi' in the mouths of its own speakers.
Latin Roots
Persian belongs to the Iranian branch of the Indo-European family, making it a distant cousin of English, Latin, and Sanskrit. The Iranian branch split from the Indo-Aryan branch sometime in the second millennium BCE. Old Persian, the language of the Achaemenid inscriptions, evolved into Middle Persian (Pahlavi), the language of the Sasanian Empire (224–651 CE), which in turn evolved into New Persian (Fārsi), the language of Ferdowsi's Shahnameh and the great medieval poets Rumi, Hafez, and Saadi.
The influence of Persian on the languages of Asia is immense. For centuries, Persian served as the lingua franca of a cultural zone stretching from Turkey to India. It was the court language of the Mughal Empire in India, the literary language of Ottoman elites, and the administrative language of Central Asian khanates. This prestige left deep marks: Turkish borrowed thousands of Persian words, Urdu and Hindi are permeated with Persian vocabulary (including everyday words like 'dost' (friend) and 'zindagi' (life)), and even Malay and Swahili show traces of Persian contact.
The English borrowings from Persian are more numerous than most English speakers realize. Words like 'paradise' (from Old Persian 'pairi-daeza,' an enclosed garden), 'bazaar' (from Persian 'bāzār'), 'caravan' (from 'kārvān'), 'chess' (from 'shāh,' king — via Arabic), 'checkmate' (from 'shāh māt,' the king is dead), 'khaki' (from 'khākī,' dusty), 'pajama' (from 'pāy-jāma,' leg-garment), and 'scarlet' (probably from 'saqirlāt') all trace back to Persian.
Greek Origins
Today, Persian in its various forms is spoken by over 110 million people. In Iran it is called Farsi, in Afghanistan it is called Dari, and in Tajikistan it is called Tajik (written in Cyrillic script). Linguistically these are varieties of a single language, though political borders have encouraged the development of distinct national standards. The question of whether to call the language 'Persian' or 'Farsi' in English is itself contested: the Academy of Persian Language and Literature in Tehran recommends 'Persian' for English-language contexts, noting that English has always used exonyms (we say 'German,' not 'Deutsch'; 'Greek,' not 'Ellinika'), but 'Farsi' has gained ground in popular English usage since the 1979 Iranian Revolution.