永 is not a word in itself, it's just a character with that meaning. The most common words you are looking for are probably 永遠、永久。I'm not quite sure about the exact difference but I think that 永遠 probably fits the English meaning of eternal a little better.
Maybe it's just me, but 永遠 sounds more emotional and 永久 has more of a meaning like "permanent" to me. Anyway, I could be totally off with this since I'm not a native speaker
