Origins
The word 'pamphlet,' meaning a small booklet on a single subject, has one of the most charming etymologies in the English language: it derives from the personal name of a fictional character in a medieval love poem. The word entered English in the fourteenth century from Anglo-Latin 'pamphiletus,' a diminutive of 'Pamphilus,' the title character of the twelfth-century Latin poem 'Pamphilus, seu de Amore' (Pamphilus, or About Love). The name 'Pamphilus' itself comes from Greek 'pamphilos' (loved by all), from 'pan-' (all) and 'philos' (loving, dear), from PIE *bʰil- (harmonious, friendly).
The poem 'Pamphilus de Amore' was enormously popular throughout medieval Europe, widely read and imitated from the twelfth through the fifteenth centuries. It tells the story of the young man Pamphilus and his pursuit of the maiden Galatea, aided by the go-between Venus. The poem circulated as a short, unbound text — too brief to be bound as a proper book, too long to be a single sheet. These small, unbound publications became so closely associated with the poem that 'pamphilet' (little Pamphilus) became the generic term for any similar short publication, regardless of content.
The transition from a character's name to a word for a type of publication parallels other such transformations in English. 'Atlas' (a book of maps, named for the mythological titan often depicted on the frontispiece), 'algorithm' (from the name of the Persian mathematician al-Khwarizmi), and 'dunce' (from the philosopher John Duns Scotus) all show how names can become common nouns. In each case, the person or character was so closely associated with a practice, an object, or a quality that their name absorbed the meaning entirely.
Development
The pamphlet has played a disproportionate role in political and intellectual history relative to its modest physical form. Martin Luther's ninety-five theses (1517) circulated as a pamphlet. Thomas Paine's 'Common Sense' (1776), which argued for American independence, was a pamphlet that sold approximately 500,000 copies. The pamphlet wars of the English Civil War produced thousands of polemical pamphlets that shaped public opinion and democratic discourse. The French Revolution was fueled by pamphlets. In each case, the pamphlet's advantages were the same: cheap to produce, easy to distribute, quick to read, and difficult for authorities to suppress.
The Greek prefix 'pan-' (all, every) in 'Pamphilus' has been extraordinarily productive in English: 'pandemic' (affecting all people), 'panacea' (a cure for all diseases), 'panorama' (a view of all), 'pantheism' (all is god), 'Pandora' (all-gifted), 'pandemonium' (a place for all demons, coined by Milton), and 'pantomime' (imitating all). The root 'philos' (loving) has generated an equally vast family: 'philosophy' (love of wisdom), 'philanthropy' (love of humanity), 'bibliophile' (book lover), and 'Philadelphia' (brotherly love).
The word 'pamphlet' thus encodes a miniature cultural history: a Greek name meaning 'loved by all' attached to a fictional lover in a medieval Latin poem, transferred to the type of publication in which that poem circulated, and eventually applied to one of the most powerful instruments of political communication in human history. That a word born from a love story became the name for the vehicle of revolution and reform is one of etymology's more pleasing ironies.