In general, a "staple" is either a metal fastener or a principal product or need. The first meaning is derived from the Old English "stapol," which means "post" or "pillar." The second is derived from the Middle Dutch "stapel," which means "market."
Metal Fasteners
Staples are most commonly known as metal fasteners. Whether they are the ones found in office supply stores or the heavy duty ones found in hardware stores, they all have the same basic design. A short piece of metal is sharpened on both ends and then bent into a "U" shape. Some are sold individually and are driven in with a hammer, but staples are usually glued together in strips and driven in with a stapler. The word is also used as a verb when talking about the use of staples.
Examples
The electrician secured the cable with staples.
The assistant collated the copies and stapled them together.
The carpenter's job was made easier when he purchased a new staple gun.
Principal Products
The idea of a staple as a principal product has evolved into many branches over the years. Since it is derived from a word meaning "market," staple started out meaning the principal product sold at a market. It then came to mean the principal necessity of a person's diet. From there, it came to mean a principal necessity in a more generic sense. Now, it is often also used in an even more generic sense to describe the primary item within a group.
Examples
The Forbes' Meat Market staple is smoked sausage.
Potatoes are an Irish staple.
Most small markets will carry staples such as milk, bread, butter and eggs.
The car chase scene is a staple in action movies.
Anomaly
There is also a definition for "staple" that is used only within the textile industry. Cotton, wool, flax and other fibers are graded by their length, or "staple." In general, fibers are divided into "short-staple" or "long-staple," but their measured length is the actual staple used to grade the fiber.
