I think I know the word to modify, and from Google Translate this seems to give three options for latin words. These mean "for a price", "look back" and "secret", none of which seem to fit. Am I barking up the wrong tree?
You're barking at exactly the right spot Sloth. It's the last of those. If you slightly modify the translation to English it makes sense both in terms of the title of the puzzle and as a component of the achievement.