n.

1. the most extreme possible amount or value;
   extremum
   
   • voltage peak
2. the period of greatest prosperity or productivity;
   flower, prime, heyday, bloom, blossom, efflorescence, flush
3. the highest level or degree attainable; the highest stage of development;
   acme, height, elevation, pinnacle, summit, superlative, meridian, tiptop, top
   
   • his landscapes were deemed the acme of beauty
   • the artist's gifts are at their acme
   • at the height of her career
   • the peak of perfection
   • summer was at its peak
   • ...catapulted Einstein to the pinnacle of fame
   • the summit of his ambition
   • so many highest superlatives achieved by man
   • at the top of his profession
4. the top point of a mountain or hill;
   crown, crest, top, tip, summit
   
   • the view from the peak was magnificent
   • they clambered to the summit of Monadnock
5. a V shape;
   point, tip
   
   • the cannibal's teeth were filed to sharp points
6. the highest point (of something);
   vertex, apex, acme
   
   • at the peak of the pyramid
7. a brim that projects to the front to shade the eyes;
   bill, eyeshade, visor, vizor
   
   • he pulled down the bill of his cap and trudged ahead

v.

1. to reach the highest point; attain maximum intensity, activity
   
   • That wild, speculative spirit peaked in 1929

adj.

1. of a period of maximal use or demand or activity
   
   • at peak hours the streets traffic is unbelievable