from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Obsolete form of invulnerable.
from the GNU version of the Collaborative International Dictionary of English
- adj. Invulnerable.
un- + vulnerable (Wiktionary)
Heroes is pretty watchable apart from the really dreadful bad science 'humans only use 10% of their brains' so that's obviously why some people can suddenly start to fly or be unvulnerable and such.