n. In a piece of lumber, a knothole is a void left by a knot in the wood; such holes are often convenient for peering through when they occur in fences.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a hole in a board where a knot came out
Word Usage
"This kind of problem is called a knothole, or a block of stacked characters."