Loyal comes from the Old French word loial which means something like “legal”. If someone is only loyal to you because the law requires them to be, that’s not authentic loyalty, which should come from the heart – – not contractually bound.
Similar: allegiance, faithfulness, fidelity, obedience, steadfastness, trueness, trustworthiness, commitment, dedication
Opposite: disloyalty, treachery, faithlessness, falseness, inconsistency