Sentinel
Definition 1 of 3
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Visual Imagery
Think of a sentinel as an observer who carefully watches over a specific area or object. A motion sensor acted as a silent sentinel, triggering the alarm.
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Personification
Sentinel can be used to describe non-human entities that act as guards, like security systems. The lighthouse served as a sentinel for the safe return of sailors.
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Metaphoric Use
Used metaphorically, 'sentinel' implies vigilance and an imposing or protective presence. The tall cypress trees stood like sentinels around the ancient villa.