Select the most appropriate synonym of the given word.
Fatal

The correct answer is Deadly.

Explanation:
1. Analyze the given word: The word Fatal is an adjective that describes something causing or capable of causing death, disaster, or ruin (e.g., "a fatal dose" or "a fatal mistake").
2. Evaluate the options:
- Deadly: This adjective means causing or able to cause death or serious harm. Since it shares the exact same primary meaning as "fatal", it is the most appropriate synonym.
- Additional: This means added, extra, or supplementary. It does not relate to death or disaster.
- Easy: This means requiring little effort or presenting few difficulties, which is unrelated to "fatal".
- Jovial: This means cheerful, friendly, and joyous, which is completely opposite in tone and meaning.
3. Conclusion: Therefore, Deadly is the correct synonym.