Concept:
A synonym is a word that has the same or nearly the same meaning as another word.
Step 1: Meaning of nefarious.
Nefarious means:
• Wicked.
• Evil.
• Criminal.
• Extremely immoral.
Step 2: Meaning of heinous.
Heinous means:
• Shockingly evil.
• Extremely wicked.
• Atrocious.
Step 3: Compare the meanings.
Gentle means kind.
Virtuous means morally good.
Magnificent means grand or splendid.
Only heinous closely matches the meaning of nefarious.
Step 4: Conclusion.
Hence, the correct synonym is
heinous.