What is the prefix to world extra?

There isn't a single, universally accepted prefix for "world extra". It's possible you're thinking of something else or there is a specific context where this phrase is used.

To help me understand what you're looking for, could you provide more information? For example:

* What is the full phrase or sentence you're trying to complete?

* What is the context of this phrase? Is it a news headline, a book title, a product name, etc.?

* What kind of prefix are you looking for? Are you looking for a Latin prefix, a Greek prefix, or something else?

Once I have more information, I can give you a more accurate and helpful answer.