peak1
  
  n.
    - the pointed top of a mountain. 
▸a mountain with a peak.
 - the point of highest activity or achievement. 
▸a point in a curve or on a graph, or a value of a physical quantity, which is higher than those around it.
 - Brit. a stiff brim at the front of a cap.
 - the upper, outer corner of a sail extended by a gaff.
 
v.
 reach the highest point.
adj.
 maximum or utmost:
 at peak fitness.
 ▸characterized by maximum activity or demand:
 peak hours.
 
  Derivative
  
  Etymology
  C16: prob. a back-form. from peaked, var. of dial. picked ‘pointed’.
 
  
    
peak2
  
  v.
 archaic decline in health and spirits.
 
  Etymology
  C17: of unknown origin.