in this book one word would make people magical and if you had more than one word you became more powerful. There was a limitation in that if more than one person knew the word it was rendered less effective. I remember reading the first book in what seemed to be a series but lost track and now that is all i remember.
Dave Duncan, the "A Man of His Word" series. Main characters: Rap, Inos. http://daveduncan.com/books/books.php
This GoodReads review of the first book explains the premise of how the words work, matching the questioner's details:
the source of all magic appears to be these words of power. If you know one then you're super-human in some way [...] A second word makes you great at all human endeavors, and super-human feats like forsight and such tend to go with a second word. A third makes you a sorcerer with arcane powers. [...] However, each person who knows a Word shares the power of the Word - so the more people who know the Word the less power you have