Meaning of witness corner

wit'ness cor"ner

Pronunciation: [key]
— Survey. Survey.
  1. a point, marked by a monument, situated at a known distance from and bearing relative to a corner that is used as a reference point but on which it is impossible to place a monument. Cf.(def. 10a).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.