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peak 1

1. A tapering, projecting point; a pointed extremity: the peak of a cap; the peak of a roof.
a. The pointed summit of a mountain.
b. The mountain itself.
a. The point of a beard.
b. A widow's peak.
4. The point of greatest development, value, or intensity: a novel written at the peak of the writer's career. See Synonyms at summit.
5. Physics The highest value attained by a varying quantity: a peak in current.
6. Nautical
a. The narrow portion of a ship's hull at the bow or stern.
b. The upper aft corner of a quadrilateral fore-and-aft sail.
c. The outermost end of a gaff.
v. peaked, peak·ing, peaks
1. Nautical To raise (a gaff) above the horizontal.
2. To bring to a maximum of development, value, or intensity.
1. To be formed into a peak or peaks: Beat the egg whites until they peak.
2. To achieve a maximum of development, value, or intensity: Sales tend to peak just before the holidays.
Approaching or constituting the maximum: working at peak efficiency.

[Probably Middle English pike, peke; see pike5.]

peak 2

intr.v. peaked, peak·ing, peaks Archaic
To become sickly, emaciated, or pale.

[Origin unknown.]
References in classic literature ?
First, when used as a fin for progression; Second, when used as a mace in battle; Third, in sweeping; Fourth, in lobtailing; Fifth, in peaking flukes.
Excepting the sublime breach --somewhere else to be described --this peaking of the whale's flukes is perhaps the grandest sight to be seen in all animated nature.
There it fell with mighty splash, one jagged end peaking out above the surface, while the waters bubbled and foamed with far-circling eddy.