Final answer:
The correct 3-letter synonym for caviar is 'roe'. Roe refers to the eggs of fish and certain marine animals, similar to caviar, which is specifically sturgeon roe. Other options like 'fin', 'cod', and 'hag' are not synonyms for caviar.
Step-by-step explanation:
The 3-letter synonym for caviar is roe. Caviar is a delicacy consisting of salt-cured fish eggs. These eggs, or roe, can come from different species of fish, the most prestigious being sturgeon. The term 'roe' refers to the fully ripe internal egg masses in the ovaries of fish and certain marine animals, whereas 'caviar' specifically refers to the roe from wild sturgeon in the Caspian Sea and Black Sea.
When considering the options provided, 'fin', 'cod', and 'hag' do not serve as synonyms for caviar. 'Fin' is related to the external appendages used by fish for swimming, 'cod' is a type of fish, and 'hag' is completely unrelated, often used to refer derogatorily to an old woman.