Step 1: Meaning of ‘jealous’.
The word “jealous” means feeling resentment or envy because of someone else’s success, possessions, or qualities.
Step 2: Analyze the options.
- Zealous: Means passionate or enthusiastic, not the same as jealous.
- Callous: Means emotionally insensitive, unrelated.
- Envious: Correct, as it expresses the same meaning as jealous.
- (Dangerous: Not related.
Step 3: Conclusion.
Thus, the synonym of “jealous” is “envious.”
Final Answer:
\[
\boxed{\text{Envious}}
\]