What is the meaning of the Latin-derived word "fidelity"?
And the answer: faithful.
Fidelity’s etymology goes back as far as the 15th century through Middle English, Middle French, and finally through the Latin verb "fidere," which means “to trust." Today, the word fidelity is used to refer to faithfulness in a variety of contexts — from marriage to ethics — and is commonly used in broadcast to refer to the "faithfulness" of the live sound or picture represented.
A faithful friend is loyal and steadfast— it's no wonder that many people consider their dogs to be their most faithful companions. Though "faithful" usually describes a person, you can also use it to talk about a particularly reliable object, such as your faithful pair of jeans. Another use of "faithful" connotes "remaining true to," like believers who pray and attend religious services regularly.
Indeed, as you may have guessed: the Old Faithful geyser was named in 1870 by explorer Henry Dana Washburn, surveyor-general of the Montana Territory, in reference to the regularity of its outbursts. However, despite popular belief, the geyser doesn’t erupt every hour on the hour. It currently erupts every 91 minutes on average— a length of time that has actually grown in recent years. In the 1960s, the average interval between eruptions was 66 minutes. It is uncertain what is causing the change, but the National Park Service attributes lengthening intervals to earthquake activity, which can affect the structure of the water system below ground. Does that still make it "faithful?" You be the judge.
Learn more about the etymology of "faithful" here.