Step 1: Understanding the Question:
The question asks us to identify a synonym, which is a word that shares the same or a very similar meaning with the given word 'ABANDON'.
Step 2: Detailed Solution:
First, let's establish the core meaning of the given word.
"Abandon" means to leave completely and finally, to desert, or to give up entirely.
Now, let us evaluate the meaning of each option provided:
(A) Retain: This means to continue to have something, or keep possession of it. This is an antonym, not a synonym.
(B) Forsake: This means to renounce, leave behind, or abandon someone or something. This matches the target meaning perfectly.
(C) Protect: This means to keep safe from harm or injury. This is unrelated and somewhat opposite in context.
(D) Defend: This means to resist an attack made on someone or something. This is also unrelated.
Therefore, 'Forsake' is the correct synonymous choice.
Step 3: Final Answer:
The synonym of ABANDON is Forsake.