n. The fortified tower of a motte or early castle; a keep.
the GNU version of the Collaborative International Dictionary of English
n. The chief tower, also called the keep; a massive tower in ancient castles, forming the strongest part of the fortifications. See Illust. of castle.
The Century Dictionary and Cyclopedia
n. The inner tower, keep, or stronghold of a castle. See cut under castle.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. the main tower within the walls of a medieval castle or fortress
Word Usage
"It held meetings in our big vault, which they called the donjon keep, and, naturally, when one of them was going on, boys were scarcer around the office than hen's teeth."