An idiom is a figure of speech that means something other than its literal meaning. But where do these weird phrases ("break a leg," "silver lining," "beat a dead horse") come from? Here are a few explanations:
"Riding shotgun": English speakers use it to mean is sitting in the passenger seat of a car. The phrase dates back to the early 1900s in the Wild West, when the person sitting beside the driver in coach would often carry a shotgun for protection.
"Win hands down": Refers to the fact that a jockey far enough ahead can still win a race even if he took his hands off the reins.
"Close, but no cigar": In the 1930s, cigars were given as prizes at fairs.
"Barking up the wrong tree": In the early 1800s, dogs were more commonly used for hunting. When a dog would identify prey that had run up a tree, the dog would bark upward toward it. When the prey jumped to a different tree, the dog would be left at the base of the original tree, confused, barking up to nothing.