Sentence:  Across the front of a yard and down the side , they were <WSD>iron</WSD> , either spiked along the top or arched in half circles . 
Meaning of the word marked with <WSD> tags:  a heavy ductile magnetic metallic element; is silver-white in pure form but readily rusts; used in construction and tools and armament; plays a role in the transport of oxygen by the blood