Q. Where did we get the word "wig" for a fake head of hair?
A. In the early 16th century, it was fashionable for women, and later for men, to wear a headpiece of artificial hair called a "periwig." "Periwig" developed from the earlier "perwyke," a modification of the Middle French "perruque," from Old Italian "perruea," meaning "head of hair." "Periwig" became simply wig through what etymologists call clipping or truncation. These terms denote primarily the process whereby an appreciable chunk of a word is omitted, leaving what is sometimes called a stump word. When it is the end of a word that is lopped off, the process is called back-clipping: thus examination is docked to give exam. Less common in English are fore-clippings, in which the beginning of a word is dropped, as with wig. Very occasionally we see a sort of fore-and-aft clipping, as when flu was derived from influenza.
Clipping is an ongoing process in the history of English. Its products tend to have a probational status at first - witness Swift's famous denunciation of mob when that word was newly clipped from Latin "mobile-vulgus" (fickle populace) - but may in time be absorbed wholly into the language. We may distinguish several stages in the process.
The most solid state of acceptance of a clipped form comes when many speakers no longer even know what the earlier and longer form of the word was. Thus chap, meaning fellow, no longer evokes its antecedent chapman, an old term for a merchant. A hack, meaning a cab, has for most speakers cut its historical ties with hackney, which originally designated a kind of horse. Similar remarks apply to pants (from pantaloons), cinema (from cinematograph) and many others. Status as a completely independent word is further enhanced when the phonetic substance of the word is also altered, as when perambulator (baby carriage) yielded pram, not "peram," and geneva gave rise to gin.
The status of a clipping is more provisional when speakers can in general tell you right off what word it was clipped from. Exam, gym, lab, ad, and mike are all very familiar words and must be considered part of the standard language, but anyone who knows the words at all can probably tell you where they come from, and the very availability of a recognizable longer source word makes their shorter offspring seem somewhat more informal. Just how breezily curtailed a word feels varies in ways not altogether predictable: somehow math sounds more formal than "chem" for chemistry or "sosh" for sociology.
Finally, there are clippings that are frankly slangy and not, or not yet, seriously applying for citizenship in the standard lexicon. Such are "vac" for "vacation" and "caf" for "cafeteria."
Q. When I was little, everyone told me I was the spitting image of my dad. It used to drive me nuts, but now, years later, I'm more interested in where the expression "spitting image" comes from. Can you help?
A. The original phrase is "spit and image," meaning, as the present phrase does, "a person strikingly like another person." The phrase developed from a use of the noun spit to mean "a perfect likeness." This sense of spit, first recorded in 1825, still occurs in British English but has fallen into disuse in the United States. It apparently developed from the familiar verb spit by way of a once popular saying that a son with a great resemblance to his father looked as much like him as if he had been spit out of his mouth. (Why being spit out of your father's mouth would make you look like him is a question we can't answer.)
Not everyone accepts the above explanation. Some have claimed that the phrase is actually a corruption of the phrase "spirit and image," pronounced by southern speakers in such a way that "spirit" came eventually to be understood as "spit." It may be that some such process had an influence in the ultimate development of the phrase, but lack of evidence makes it impossible to say that for certain.
"Spitting image" was first recorded in 1901. Other variants, now extremely rare, are "spitten image" and "splitting image." For a time, "spitting image" was commonly cited as an error, but it has long since established itself as a standard, if somewhat informal, phrase.