Paganism and heathenry are blanket terms which have come to connote a broad set of spiritual or religious beliefs and practices of natural or polytheistic religions, as opposed to the Abrahamic monotheistic religions. "Pagan" is the usual translation of the Islamic term mushrik, which refers to 'one who worships something other than God'. Ethnologists do not use the term for these beliefs, which are not necessarily compatible with each other: more useful categories are shamanism, polytheism or animism. Often, the term has pejorative connotations, comparable to heathen, infidel and kafir in Islam.
During the expansion of the Sokoto Caliphate in West Africa, Islamic Fulbe (Fula) labelled their non-Muslim neighbours, such as this Kapsiki diviner, Kirdi, or "pagans".
The term pagan is from Latin paganus, an adjective originally meaning "rural", "rustic" or "of the country." As a noun, paganus was used to mean "country dweller, villager." From its earliest beginnings, Christianity spread much more quickly in major urban areas (like Antioch, Alexandria, Corinth, Rome) than in the countryside (in fact, the early church was almost entirely urban), and soon the word for "country dweller" became synonymous with someone who was "not a Christian," giving rise to the modern meaning of "pagan." In large part, this may have had to do with the conservative nature of rural people, who were more resistant to the new ideas of Christianity than those who lived in major urban centers.
"Peasant" is a cognate, via Old French paisent. (Harry Thurston Peck, Harper's Dictionary of Classical Antiquity, 1897; "pagus").
In their distant origins, these usages derived from pagus, "province, countryside", cognate to Greek "rocky hill", and, even earlier, "something stuck in the ground", as a landmark: the Proto-Indo-European root pag- means "fixed" and is also the source of the words "page", "pale" (stake), and "pole", as well as "pact" and "peace".
Later, through metaphorical use, paganus came to mean 'rural district, village' and 'country dweller' and, as the Roman Empire declined into military autocracy and anarchy, in the 4th and 5th centuries it came to mean "civilian", in a sense parallel to the English usage "the locals". It was only after the Late Imperial introduction of serfdom, in which agricultural workers were legally bound to the land (see Serf), that it began to have negative connotations, and imply the simple ancient religion of country people, which Virgil had mentioned respectfully in Georgics. Like its approximate synonym heathen (see below), it was adopted by Middle English-speaking Christians as a slur to refer to those too rustic to embrace Christianity. Additionally, a lot of rural parts of Europe were the most resistant to forced Christian conversions, militarily resisted Christian Europe and stubbornly held to their natural religions reamplifying the medieval use of the term.
Neoplatonists in the Early Christian church attempted to Christianize the values of sophisticated pagans such as Plato and Virgil. This had some influence among the literate class, but did little to counter the more general prejudice expressed in "pagan".
While pagan is attested in English from the 14th century, there is no evidence that the term paganism was in use in English before the 17th century. The OED instances Edward Gibbon's Decline and Fall of the Roman Empire (1776): "The divisions of Christianity suspended the ruin of paganism." The term was not a neologism, however, as paganismus was already used by Augustine.
The urbanity of Christians is exemplified in Augustine's work, The City of God, in which Augustine consoled distressed city-dwelling Christians over the fall of Rome. He pointed out that while the great 'city of man' had fallen, Christians were ultimately citizens of the 'city of God.'
Many Slavic peoples, especially Eastern Slavs, use the word "pagan" as an insult in their language; translating roughly as a "conniving brute." The etymology of this meaning lies in the fact that after their forced conversion by western Christians, much of the Slavic lands took a dim view of the remaining non-Christians in their midsts.