1. in a way that breaks trust or loyalty; dishonestly or treacherously
2. in a way that is not accurate or true to the original

Examples

• He acted unfaithfully by revealing company secrets to competitors.
• She unfaithfully betrayed her friend’s confidence.
• The translator unfaithfully changed the meaning of the original text.
• The actor unfaithfully portrayed the historical figure.
• The employee unfaithfully violated his oath of loyalty.
• The adaptation unfaithfully departed from the source material.
• He unfaithfully broke his promise to help with the project.