means A tall structure built so guards can survey the surrounding land and spot danger — approaching enemies, fires, intruders — from a distance.

from A plain English compound of "watch" and "tower," and both halves are old. "Watch" descends from Old English wæcce, the act of staying awake and keeping vigil — a cousin of "wake" — while "tower" comes through Old French tur from Latin turris, the Romans' word for a high fortified structure. Bolt the two together and you get exactly what it says: a tower where someone keeps watch. The pairing has been doing duty in English for centuries, long enough to climb out of the literal battlements and into scripture, poetry, and the names of countless lookout posts.