What is a portmanteau word?

A portmanteau blends the sounds and meanings of two words into one: breakfast and lunch give brunch, smoke and fog give smog, motor and hotel give motel, iPod and broadcast give podcast, and spoon and fork give spork. The term comes from Lewis Carroll, who has Humpty Dumpty explain the invented words in Jabberwocky to Alice by saying there are two meanings packed up into one word, like a portmanteau, which was a suitcase that opened into two compartments. Slithy, he explains, is lithe and slimy.

The device is distinct from a compound, where two whole words join without losing material, as in bookstore or greenhouse, and from an acronym or initialism, where letters stand for words. It is also distinct from a clipping, where a word is simply shortened. Portmanteaus tend to be productive during periods of rapid technological or cultural change, which is why so many recent ones come from technology and internet culture, including malware, emoticon, webinar, and the entire genre of celebrity couple names.

Two notes on how they behave. Many become so thoroughly naturalized that speakers stop perceiving the seam, and most people using motel, smog, or bit, which fuses binary and digit, are not thinking of the components at all. And English is comparatively hospitable to them because its morphology is flexible, while languages with stricter word formation rules generate them less readily. Not every blend survives, and the ones that do tend to fill a genuine lexical gap concisely, which is a reasonable predictor of whether a newly coined one will last beyond the marketing campaign that produced it.