Ultra-rare (dict)

Twilight Dictionary

ultra-rare

n. An informal term for a handful of items in the game which are exceptionally uncommon finds, such as the Boomstick or the Ebon Eye of the Deep, these items are ironically neither ultra nor rare, but they most certainly are 'a rat ruler.' Wait, that doesn't sound right ...

Ultra-rares are considerably harder to find than semi-rares, and generally have very limited ways to improve one's odds of getting one.

Source

Item descriptions of geologist's rifle and chronatomic clock