IPA: /ˈwɒtʃˌtaʊə/
KK: /ˈwɑːtʃˌtaʊər/
A tall structure used for observing an area, often where a guard or lookout can watch for dangers or important events.
The soldiers climbed the watchtower to keep an eye on the surrounding area.
Watchtower → It is formed from "watch" (from Old English *wæccan*, meaning to be awake or to watch) and "tower" (from Old French *tor*, meaning a tall structure). A watchtower is a tall structure used for watching or observing from a height.
Think of being 'awake' ('watch') in a 'tall structure' ('tower') to keep an eye on things — that's what a watchtower is for.
No commonly confused words.