Like many words of its kind, etymology found its way to English in the 14th century by way of Old French, at which point it simply robbed the older language of the term etimologie or ethimologie. English is quite the thief, you see.
The word made its way to French via Latin (etymologia), as is often the case, and as is even more often the case, the Latin word was adopted from the Greeks, who were the first to analyze words to find their true origin.
It is this process wherein lies the root of the word: etymon. “True sense.” That is, the Greek etymologia, composed of etymon and -logia means “the study of the true sense of a word.”
Etymon and its companion etymos (“true, real, actual”) is a cognate—a word with the same linguistic background and meaning—with the Sanskrit satyah, the Gothic sunjis, and Old English soð, all meaning “true.”
When Cicero studied etymology, he referred to it as veriloquium, also based on a word for “truth” which you can see in English words such as verily and verify. Much of our understanding of etymology is skewed or uncertain thanks to the work of Christian and pagan classical etymologyists, who used allegory and guesswork to fill blanks in the (often word-of-mouth-based) historical record.