Q followed by U
Q From Ivan Berger: In English words, the letter q is always followed by u — the only such mandatory letter pair I can recall. But it is also used in words transliterated from other alphabets (such as the Arabic qat), where the letter k would presumably work just as well. How did it achieve its rather odd status?
A It all started long before English even existed. The Phoenicians had two symbols in their alphabet for k, for the very best of reasons — in their language, as in other Semitic languages such as Hebrew and Arabic, there are two distinct k sounds, only one of which exists in English. The one we don’t have — a guttural sound at the back of the mouth — the Phoenicians represented by a symbol that they called qop (their word for a monkey). This was used in particular before vowels that are also sounded at the back of the mouth, especially o and u.
The Greeks took the Phoenician symbol over as qoppa or koppa. This isn’t in the classical Greek alphabet — it was dropped as unnecessary around 400BC, because Greek has never had the sound it represents. However, a version of the Greek alphabet that did still contain koppa was borrowed by the Etruscans (they probably got it from Greek colonists who settled in Campania). The Etruscan alphabet actually had three symbols for the k sound — gamma was used before e and i, kappa was used before a and koppa before o and u (gamma was available because Etruscans had no hard “g” sound in their language).
In turn (you’re still following my steps around the Mediterranean, I hope), the Romans took their alphabet from the Etruscans; like the Greeks, Latin had only the one k sound. As a result, over time kappa was dropped, koppa evolved into q, and gamma into c (these changes explain why Greek words spelled with k have their Latin equivalents spelled with c). The Romans used q only before u, though the combination was actually written as qv, since v was a vowel in classical Latin, to represent the kw sound that was so common in the language.
If we move on about a thousand years, we find that Old English had the same sound, but represented it by cw, since q had been left out of their version of the alphabet (so queen in Old English was spelled cwen, for example). French, however, continued the Latin qv, though by now written as qu. After the Norman Conquest, French spelling gradually took over in England, eventually replacing the Old English cw by Latinate qu, though this change took about 300 years to complete. As many writers have since pointed out, the change was unnecessary, as we don’t need qu in the alphabet any more than the English before the Norman Conquest did — cw would work as well most of the time and in those situations in which qu is said as k, as in words from French like antique, we could use c or k instead).
After all this, the reason why versions of Arabic words written in English use q without a following u is easy to understand — it’s a neat way of transcribing that guttural k sound (the Arabic letter qaf) that’s faithful to the way the alphabet has evolved over more than two millennia.