A portmanteau (plural portmanteaus or portmanteaux) is a large travelling case made of leather. These cases consist of two halves that are connected with a hinge.
In linguistics, a portmanteau word (sometimes called a blend or frankenword) is a word that is formed by combining two or more words. This meaning of the word was coined by Lewis Carroll in Through the Looking-Glass, and What Alice Found There.
An example of a portmanteau is smog, a combination of the words smoke and fog. Baseketball is also a portmanteau of the words baseball and basketball because baseketball is a mixture of the two sports. Carroll used such words to humorous effect in his poems, especially Jabberwocky. James Joyce used portmanteau words extensively in Finnegans Wake. Many corporate brand names, trademarks, and initiatives, as well as names of corporations and organizations themselves, are portmanteaux. For example, Wikipedia is a portmanteau made from wiki and encyclopedia.