The title of the poem we're looking at is 'Invictus'. It's a Latin word and like many English words, we've borrowed the original, bent it to suit ourselves and kept using in.
Take a look at the word itself. What pieces can it be broken into? What modern words can you make out of some of the pieces? These are the clues you can use to try to understand words you've never heard before.
From 'Invictus' we take 'Victorious'.
Unfortunately, the Clan Armstrong crest gives few clues as to the meaning of 'Maneo' and the word itself doesn't help much either. It means 'remain' or stay'.
I remain unvanquished.