Fidelity
Etymology
From Latin fidelitas, "faithfulness," from fidelis, "faithful," ultimately from fides, "faith, trust." The same root gives us "confide," "fiduciary," and the dog’s name Fido. At its heart the word is about trust honored over time — whether to a spouse, a principle, or, as in "high fidelity," an accurate reproduction of a sound.
noun · /fih-DEL-ih-tee/
Faithfulness — steady loyalty to a person, cause, duty, or truth.
What it names
The virtue of keeping faith: honoring your commitments and staying true to what you have pledged yourself to.
Example
His fidelity to the original text meant the translation lost none of the author’s strange, exact rhythms.
Related idea
Loyalty is allegiance to a person or group; fidelity is broader and more solemn, extending to vows, duties, and truths, not just people.
noun · /fih-DEL-ih-tee/
The degree to which a copy, recording, or reproduction matches its original.
What it names
accuracy of reproduction — the “hi-fi” in high-fidelity sound
Example
The remaster restores the recording to a fidelity the old tape never captured.
Related idea
Faithfulness to a person becomes faithfulness to a source signal; the closer to lifelike, the nearer to verisimilitude.