Select the most appropriate synonym of the given word.
Concordant

The correct answer is Harmonious.

Step-by-step Explanation:

1. Analyze the Given Word:
The word "Concordant" is an adjective that means being in agreement, agreement of sounds, or acting in harmony/concurrence. It is derived from the noun "concord," which means agreement or harmony between people or things.

2. Analyze the Options:

• Certain: Means known for sure; established beyond doubt. This is not related to agreement or harmony.
• Unanimous: Means (of two or more people) fully in agreement. While it carries a similar theme of agreement, it specifically refers to a collective opinion or vote (e.g., "a unanimous decision"), whereas "concordant" has a broader application to general agreement, consistency, or pleasant blending of elements.
• Abnormal: Means deviating from what is normal or usual, typically in a way that is undesirable or worrying. This is unrelated.
• Harmonious: Means free from disagreement or dissent, marked by agreement in feeling, attitude, or action. It also refers to things that are pleasingly or congruously combined.

3. Conclusion:
Since "Concordant" and "Harmonious" both describe things that are in complete agreement, consistent, and working together in a pleasing or peaceful manner, "Harmonious" is the most appropriate synonym.