Keep in mind that “Zei” is not an acronym for that Legendary Gem. It is an abbreviation. To keep things consistent in your table or in a guide, you should probably keep things in context. In this case, “ZSoV” would be the acronym for Zei’s Stone of Vengeance.
Just sayin’… 
Obviously, in a post during a discussion or in-game Chat, typing “Zei” would be acceptable in place of typing the whole name.