guy wire

noun, a wire or cable used to secure a tent or keep something upright (COD)

“All of a sudden this horrendous crack of lightning came down. It hit the windmill and it come down the guy wire. Len’s horse went down. I can remember it. If you hit the horse over the head with a sledgehammer, it wouldn’t go down. It just collapsed right there on the road, and the guys at the cheese factory all run out to help him with the horse, and the horse fortunately wasn’t killed.”