From the Latin "Intro Ducere"

Do you know where the word "introduce" comes from? It comes from the Latin, Intro Ducere, meaning "to guide into". As such, when you introduce you guide something into the issue being discussed, usually some new information, such as the etymology of a relevant word in that context. This happens in some works, when the etymology of words is used as a way to introduce bits of exposition, an explanation to a situation, a point or even a Reason You Suck Speech. This trope shows that the speaker is cultured, smart and - usually - in control, as most people in a pickle don't really worry about etymology. Usually starts with "Do you know where the word 'X' comes from?" - Note that the little etymology lesson must turn out to have something to do with the matter at hand.

Anime and Manga

 * Watanuki does this to a woman in xxxHolic, explaining that she doesn't love Doumeki, only admires him. Admiration, from Latin, Ad - On and Mirare - being amazed. At least, that's how it goes in Portuguese. He then proceeds to explain the Japanese etymology, and proceeds to use said little etymology lesson to make his point.

Literature
"Elves are wonderful. They provoke wonder. Elves are marvelous. They cause marvels. Elves are fantastic. They create fantasies. Elves are glamorous. They project glamour. Elves are enchanting. They weave enchantment. Elves are terrific. They beget terror. The thing about words is that meanings can twist just like a snake, and if you want to find snakes, look behind words that have changed their meaning. No one ever said elves are nice."
 * Discworld series:
 * Lords and Ladies:


 * In Men At Arms, Carrot points out that, as a policeman—from polis, city—he is a man of the city. Later, Commander Vimes says the same thing during an argument with the city's ruler, Lord Vetinari, and Vetinari responds by pointing out that "politician" has the same root.
 * In the Merry Gentry series, the narrator's monologue often explains the Gaelic origins of certain words, and connects their modern, metaphorical meaning to the ancient, literal meaning used by the fey in the story. For instance, "slogan" is a corruption of "slaugh-gairn," so called because Celtic war cries were a kind of incantation, calling on the faerie slaugh to help them. She also describes an actress as "glamorous" as a way of pointing out that her faerie power and her fame are synergistic.

Live-Action TV
"Brennan: Kriss Kringle. From the North Pole. Lives above a toy store - This is further evidence that our victim, is indeed, the mythic figure known as Santa Claus. Booth: Mythic. Coming from the Latin, "Myth", meaning "doesn't actually exist." Brennan: No. From the Greek, "Mythos", meaning "word.""
 * Bones: The Victim of the Week was a guy who seemed to really be Santa Claus. This gives them another opportunity to bicker Like an Old Married Couple. Booth's remark isn't quite From the Latin "Intro Ducere", but Brennan's correction is.


 * CSI had one when Grissom investigated the death of a man who had Down's syndrome. After catching the murderer, Grissom calls back to an earlier conversation where the murderer called the victim a "retard" (Grissom corrected him, of course) and informs him that "retard" means "to hinder", so the killer's life "just got retarded".