Disloyal; unfaithful; not true to one's duties or allegiances.
From 'dis-' (prefix negating) + 'leal' (from Old French 'leal', from Latin 'legalis', meaning 'legal' or 'lawful'). 'Leal' meant loyal, and 'disleal' inverts this meaning.
Scottish people still use 'leal' to mean loyal—you might hear 'true and leal'—which makes 'disleal' a forgotten antonym that connects to both Scottish heritage and medieval concepts of feudal duty.
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