Dotty, how exciting!
The words are Latin and form a palindromic magic square, which can be used for all sorts of magical purposes, but generally for protection of the individual. Looking at the eBay link, it seems as though it was manufactured in Mexico, but given the fact that you say the words are scratched into the lid, it sounds as though that wasn't part of the original design, but maybe done by great uncle or whoever gave it to him.
The fact that 'Alpaca' seems to be a Mexican manufacturer is curious, as Mexico has only comparitively recently been a tourist destination. Did great uncle travel to Mexico?
When was great uncle alive? Might it have been a keepsake given to him during one of the World Wars? Perhaps someone who loved him gave him the box to keep him safe. Or was great uncle a bit of a dabbler in the occult himself? All very exciting, and I'd love to know more!