W
Its name in English is spelled double-u (pronounced /ˈdʌbljuː/).
History
The earliest form of the letter W was a doubled V used in the 7th century by the earliest writers of Old English; it is from this <uu> digraph that the modern name "double U" comes. This digraph was not extensively used, as its sound was usually represented instead by the runic wynn (Ƿ), but W gained popularity after the Norman Conquest, and by 1300 it had taken wynn's place in common use.
Other forms of the letter were a pair of Vs whose branches cross in the middle. An obsolete, cursive form found in the nineteenth century in both English and German was in the form of an "n" whose rightmost branch curved around as in a cursive "v" (compare the shape of ƕ).
The sounds /w/ (spelled with U/V) and /b/ of Classical Latin developed into a bilabial fricative /β/ between vowels, in Early Medieval Latin.
In German, this phoneme /w/ later became /v/; this is why German W represents that sound. In Dutch, it became a labiodental approximant /ʋ/ (with the exception of words with EEUW, which have /eːw/), or other diphthongs containing -uw.
Usage
There are only five major European languages that use W in native words: English, German, Polish, Dutch, and Welsh.
English uses it to represent /w/, German and Polish use it for the voiced labiodental fricative /v/ (with Polish using Ł for /w/), and Dutch uses it for /ʋ/. Unlike its use in other languages, the letter is used in Welsh to represent vowels as well as consonants.
English also contains a number of words beginning with a w that is silent in most dialects before a (pronounced) r, remaining from usage in Anglo-Saxon in which the w was pronounced: wreak, wrap, wreck, wrench, wroth, wrinkle, etc. (Certain dialects of Scottish English still distinguish this digraph.)
In the International Phonetic Alphabet, /w/ is used for the voiced labial-velar approximant, probably based on English.
In the Finnish alphabet, "W" is seen as a variant of "V" and not a separate letter.
It is however recognised and maintained in the spelling of some old names, reflecting an earlier German spelling standard, and in some modern loan words. In the alphabets of modern Romance languages, W is not used, except in foreign names and words recently borrowed (le week-end, il watt, el kiwi).
When a spelling for /w/ in a native word is needed, a spelling from the native alphabet, such as V, U, or OU, can be used instead. The same was true in the Swedish and Danish alphabets until 2006 and 1980, respectively, when the letter was officially acknowledged as an individual letter.
The equivalent representation of the /w/ sound in the Cyrillic alphabet is Ў, a letter unique to the Belarusian language.
The Russians, however, use the Cyrillic character В, (/v/ the equivalent of V in the Latin alphabet), when transliterating "W".
"Double U" is the only English letter name with more than one syllable, except for the occasionally used, though somewhat archaic,"œ" (its name is pronounced similar to "ethel"). This gives the nine-syllable initialism www the irony of being an abbreviation that takes three times as many syllables to say as the unabbreviated form.
A few speakers therefore shorten the name "double u" into "dub" only, although this is rather rare and nonstandard; for example, University of Washington and University of Wyoming are both known colloquially as "U Dub", and the automobile company Volkswagen, abbreviated VW, is sometimes pronounced "V-Dub".