Something etymological relates to the way a word originated. You can look up a word's roots and the history of how it came to get its meaning in an etymological dictionary.
Etymology is the history of words, including the way they've changed through the years. The adjective etymological describes anything that has to do with etymology. Etymological research of English words often leads back to Old English, Greek, or Latin roots. The etymological origin of etymological, in fact, is Greek: the root word etymologia means "study of the true sense of a word."