Thanks, Monique. Actually that translation is a combination of what I found in the songbook where I first found the song and what I found at a couple of websites that had the lyrics to the song.   (I studied French for 2 years but we didn't deal a lot with things one might give a friar to get him to "dance" with you.)   It's possible that the book did translate "psautier" as "book of psalms," but it's been at least 20 years since I've seen that book.   

The thing that makes "sac de bur'" hard to look up is that it's a contracted form of "bure."