Real Dictionary

staple
A staple food, product, or activity is one that is basic and important in people's everyday lives.

staple in American English 1
the chief commodity, or any of the most important commodities, made, grown, or sold in a particular place, region, country, etc.
noun: a short piece of wire bent so as to bind together papers, sections of a book, or the like, by driving the ends through the sheets and clinching them on the other side
transitive verb: to secure or fasten by a staple or staples

staple in American English 2
a U-shaped piece of metal with sharp, pointed ends, driven into a surface to keep a hook, hasp, wire, etc. firmly in place
to fasten or bind with a staple or staples
adjective: chief or prominent among the products exported or produced by a country or district; chiefly or largely dealt in or consumed
noun: a principal raw material or commodity grown or manufactured in a locality
transitive verb: to sort or classify according to the staple or fiber, as wool

staple in British English 1
noun: a short length of thin wire bent into a square U-shape, used to fasten papers, cloth, etc
verb: to secure (papers, wire, etc) with a staple or staples

staple in British English 2
adjective: of prime importance; principal
noun: a staple commodity
verb: to arrange or sort (wool, cotton, etc) according to length and fineness