The term 'Guinness Superlative' refers to the Guinness World Records, which is a book that documents the world's MOST extraordinary achievements. The crossword solutions for this term are 'MOST' (4 letters), 'longest' (7 letters), 'tallest' (7 letters), 'OLDEST' (6 letters), and 'mostever' (8 letters). These words refer to the various categories of records that Guinness World Records recognizes, such as the MOST people in one place, the longest distance traveled, the tallest structure, the OLDEST living person, and the MOST ever achieved in any category.