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Meaning of onlap

on•lap

Pronunciation: (on'lap", ôn'-), [key]
— n. Geol.
  1. the advance of a sea beyond its former shore.
  2. the layer or layers of sedimentary rock formed on a sea floor as a result of this advance. Cf.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.