Loyalty
Etymology
From Old French "loial," from Latin "legalis" (legal, lawful) — the same root as "legal" and "loyal’s" cousin "leal." Loyalty began as lawfulness, fidelity to what the law required, and only later shifted to faithfulness to persons and causes. The legal ancestry hints at its bindingness: a debt one honors.
noun · /LOY-uhl-tee/
Faithful allegiance to a person, group, or cause, especially when it is tested.
What it names
Use it for the commitment that holds when it becomes costly — the virtue that only shows itself under strain.
Example
Her loyalty to the team meant she defended them in rooms where they couldn’t speak for themselves.
Related idea
Fidelity stresses keeping faith with a promise or bond, often intimate; loyalty stresses standing by someone against rivals or attack. Allegiance is more formal and hierarchical — owed to a flag, sovereign, or institution.