Explanation:

- Invincible means too powerful to be defeated or overcome. It's often used to describe someone or something that cannot be beaten.

- Option 1: declaiming - This refers to speaking loudly or passionately in a formal and rhetorical manner. It is unrelated to being unbeatable or invincible.

- Option 2: perplexing - This means causing confusion or being difficult to understand. It doesn't relate to the concept of being invincible.

- Option 3: uninspiring - This describes something that fails to motivate or excite. It is the opposite of powerful and is not similar to invincible.

- Option 4: unbeatable - This means not able to be defeated or bested. It directly matches the meaning of invincible.

Your choice, option 4: unbeatable, is indeed the word that is similar in meaning to invincible.