Definition of "watchtower"

Redcap - A malevolent goblin easily distinguishable by their namesake red cap, fiery red eyes, claws and iron boots. They often appear as little old men, but can run very fast despite the boots. They reside in castles and watchtowers along the English-Scottish border, but will move their residence to avoid detection.

2002, Cecilia Dart-Thornton, The Ill-Made Mute: The Bitterbynde‎