The word is based on a Renaissance misreading of a Greek manuscript by Cicero.
The word "syllabus" rests on a printing error. In Epistulae ad Atticum, Cicero used the Greek word sittybas (accusative plural of sittyba), meaning the parchment labels attached to the ends of scrolls listing their contents.1 When a fifteenth-century editor prepared the text for print around the 1470s, the unfamiliar Greek word was corrupted to "syllabus," and the error was reproduced in subsequent editions.
The misspelled word entered academic usage in the seventeenth century, first appearing in English around the 1650s to mean a concise table of the heads of a discourse or a summary of the subjects covered in a course of lectures.2 Pope Clement IV used the title Syllabus Errorum (Syllabus of Errors) in 1864 for a papal document condemning eighty propositions he considered heretical.3
The correct Latin plural would be "syllabi," but because the word was never actually Latin, that form is itself a construction. "Syllabuses" is the more honest English plural, though both forms are widely used.4
The modern university syllabus, a document listing readings, assignments, grading criteria, and course policies, did not become standard practice until the mid-twentieth century. Before that, course content was typically communicated verbally or posted informally. The syllabus as a contractual document between instructor and student is a recent development, driven partly by accreditation requirements and partly by the consumer model of higher education.5