As a noun, a peak is the pointed top of a mountain or the highest level of something. As a verb, it means to reach the highest point and then usually begin to decline. As an adjective, it describes something at its best or highest level.
“Peak” likely comes from Old French *pic*, meaning “sharp point,” related to “pike.” It has long been used for sharp tops of mountains and then for the height of success or activity.
We use the shape of a mountain to describe grades, careers, and even energy levels. When you say “peak performance,” you’re borrowing the image of standing on a narrow, risky top. The word quietly suggests that being at the very top is both impressive and unstable.
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