A comb or tuft on the head of a fowl; a plume, tuft, or the like, on a helmet; the ridge of a wave or of a mountain; the top of anything; head.
A coat of arms.
Once he picked these up, and looked at the crest on them. – Harding's luck by E. [Edith] Nesbit
We are on the crest of the wave, and the depression follows quickly. – A Year in the Fields by John Burroughs