watchtower \ˈ ̷ ̷ˌ ̷ ̷\noun 1. a.: a tower on which a sentinel is or may be placed : lookout b.: an observation point < from this somewhat unpromising watchtower … surveyed English life — Quarterly Review > 2.archaic: lighthouse 3.: a turret-shaped projection of the cephalothorax of a spider supporting an eye