Concept:
A synonym is a word having the same or nearly the same meaning as another word.
The word
\[
\text{Invincible}
\]
means impossible to defeat, too strong to be overcome, or unconquerable.
Step 1: Understand the meaning of the given word.
\[
\text{Invincible}=\text{cannot be defeated}
\]
A person, army, or force that is invincible cannot be easily attacked or defeated.
Step 2: Check option (A).
\[
\text{Invulnerable}
\]
means not easily hurt, harmed, attacked, or defeated.
This is very close in meaning to invincible.
Step 3: Check other options.
\[
\text{Inevitable}
\]
means certain to happen.
\[
\text{Invisible}
\]
means cannot be seen.
\[
\text{Individual}
\]
means a single person or separate thing.
These words do not match the meaning of invincible.
Step 4: Final answer.
\[
\boxed{\text{invulnerable}}
\]