- The fortified main tower of a castle; a keep.
- The inner tower, keep, or stronghold of a castle. See cut under <internalXref urlencoded="castle">castle</internalXref>.
- The chief tower, also called the <altname>keep</altname>; a massive tower in ancient castles, forming the strongest part of the fortifications. See <ex>Illust.</ex> of <xref urlencoded="castle">castle</xref>.
- The <xref>fortified</xref> <xref>tower</xref> of a <xref>motte</xref> or early <xref>castle</xref>; a <xref>keep</xref>.
- the main tower within the walls of a medieval castle or fortress