Djew is ancient Egyptian for "mountain", making it ReeToes' favourite slang for Mountain Dew, her favourite beverage. Blame Mutt for finding out and telling Ree.
On the Pro boards, especially the Cross'd Roads inns, Djew is a carbonated, caffeinated, sugared, non-copyright-infringing soft drink. It comes in ceramic bottles with medium-length necks, shipped in papyrus crates from somewhere vaguely sandy.
Didn't it also come in cans? I could swear that Jaina's first Djew was canned.