Final answer:
The 8-letter word for the highest point of success or the highest part of a rock formation is 'zenith.' It is also used in astronomy to denote the point directly above an observer and can refer to the climax in literature or the highest point of a mountain, like Mount Everest.
Step-by-step explanation:
The 8-letter word for the highest point of success or the highest part of a rock formation is zenith. The word pinnacle can also mean a peak or summit but it is not 8 letters. Summit and apex are similar in meaning; however, they do not meet the requirement of being 8 letters long. The word zenith is used not just to describe the highest point of success or achievements but also in astronomy, where it denotes the point on the celestial sphere directly above an observer. In literature, the word climax can refer to the peak of action in a story. When talking about mountains, the tallest peak on Earth, Mount Everest, represents a literal peak or zenith in terms of height.