Gatepost refers to the physical side supports of a gate, made from various materials. The old iron gate creaked as it swung from the stone gateposts.
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Standing Point
'Leaning against a gatepost' can suggest someone waiting or at rest, often found in rural or farm settings. He was just standing there, leaning against a gatepost, lost in thought.
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Metaphorical Use
Gatepost could metaphorically represent a strong point to rely on, similar to a dependable person. In tough times, she was the gatepost everyone clung to.