The word for the study of word origins started out as a claim about truth.
Greek etymon meant "true sense" or "original meaning." It is the neuter form of etymos, "true, real, actual." Add -logia, "study of," and etymologia was the analysis of a word to find what it truly meant. Etymonline notes that Cicero translated the Greek word into Latin as veriloquium, literally "true speaking."
Behind the name sat an idea: that the earliest form of a word carried its correct meaning. The Stoics searched for the etymon, which they considered the first form of a word. Encyclopedia.com adds that they thought languages were slowly declining from an earlier perfection.
The method was loose. Isidore of Seville, writing in Spain in the 7th century, compiled a 20-part work called the Etymologiae. He linked Latin homo, "man," to humus, "soil," because God made man from clay. That is a link made by sound and symbolism, and today it counts as folk etymology. Etymonline says the field suffered in reputation for about a thousand years because classical etymologists relied on allegory and guesswork.
English first records the word in the late 14th century, through Old French. Etymonline notes a strange early sense: the "conjugation and categorization of words," probably from a misreading of the term as dealing with verb tenses. The OED now labels that meaning historical.
Etymonline dates the sense of a branch of linguistics, dealing with how words originate and change, to the 1640s. Later scholars compared related languages and reconstructed lost ancestors, which made etymology part of historical linguistics. Encyclopedia.com quotes Max Müller in 1880: "The etymology of a word can never give us its definition."
So modern linguists keep the name and reject its premise. A word's origin is a fact about its history, not a hidden key to what it means today. The word kept its old claim to truth even after its practitioners stopped believing it.