"Cadogan" is the English name for a lidless teapot, inspired by Chinese "wine pourer" pots, which are to be filled from the bottom. (That is, it's all one piece and the opening for filling is at the bottom of the design; it contains a tube inside which runs up to near the top. Once it is filled, it is turned right side up again, and tea comes out through the spout like a standard teapot.) The name comes from William Cadogan, 1st Earl of Cadogan (1675-1726), who was said to be the first Englishman to own such a pot. They became trendy in late 18th-century England. However, they were also made in other parts of Europe after the Chinese example spread; the Italian name for the same type of pot, for instance, is "vaso senza bocca."
The Earl of Cadogan was also the source for another meaning of the word: "ponytail tied at the back with a ribbon, rubber band, or piece of string based on an 18th-century portrait featuring him." Wigs in the Cadogan or "Club" style became popular in the 1770s.
The Cadogan is also the name of a London hotel, built in the late Victorian era on on Sloane Street in Knightsbridge; actress Lillie Langtry lived here, and it is where Oscar Wilde was arrested in 1895. The name has also gone to the city of Cadogan in Alberta, Canada; Cadogan Holidays, a British travel agency; Cadogan Guides, a series of travel guidebooks; Cadogan Contemporary, an art gallery in London; the Cadogan Group, "a Belfast-based group promoting discussion and analysis of the political situation in Northern Ireland"; and numerous other businesses. Berek tells me that "The Scottish Refugee Council is based at Cadogan Square in Glasgow. There is also a Cadogan Street. Both are near the city's Central station."
Sources:
http://www.wordsmith.org/awad/archives/0104
http://www.anteques.com/srv/antaday/1113.htm
http://www.users.waitrose.com/~beryls/Pages/lw1_8.htm
http://nemmelgebmurr.com/vintage/squirrel.html
http://www.costumes.org/history/100pages/18THHAIR.HTM
http://www.sayreschool.org/5thgrade/Colonial/Wig_conley.htm
http://hera.romance-central.com/creativecorner2.htm
http://www.cadogan.com/
http://homepages.gold.ac.uk/oscholars/vol_iii_08/music.html
http://www.centralalberta.worldweb.com/Cadogan/
http://www.cadoganholidays.com/
http://www.cadoganguides.com/
http://www.artcad.co.uk/
http://www.cadogan.org/