The English word is first attested in the early 17th century, from Modern Latin syncretismus, drawing on Greek συγκρητισμός (synkretismos), supposedly meaning "Cretan federation", but this is a spurious etymology from the naive idea in Plutarch's 1st-century AD essay on "Fraternal Love (Peri Philadelphias)" in his collection Moralia (2.490b). He cites the example of the Cretans, who compromised and reconciled their differences and came together in alliance when faced with external dangers. "And that is their so-called Syncretism [Union of Cretans]". More likely as an etymology is sun- ("with") plus kerannumi ("mix") and its related noun, "krasis," "mixture."
Erasmus probably coined the modern usage of the Latin word in his Adagia ("Adages"), published in the winter of 1517–1518, to designate the coherence of dissenters in spite of their differences in theological opinions. In a letter to Melanchthon of April 22, 1519, Erasmus specifically adduced the Cretans of Plutarch as an example of his adage "Concord is a mighty rampart".