used for "London Metropolitan Police," 1864, from the name of short street off Whitehall, where from 1829 to 1890 stood the headquarters of the Metropolitan Police Force, hence, the force itself, especially the detective branch. After 1890, it was located in "New Scotland Yard."
a late-developing letter in English. Called ipsilon in German, upsilon in Greek, the English name is of obscure origin. The sound at the beginning of yard, yes, yield, etc. is from Old English words with initial g- as in got and y- as in yet, which were considered the same sound and often transcribed as Ȝ, known as yogh. The system was altered by French scribes, who brought over the continental use of -g- and from the early 1200s used -y- and sometimes -gh- to replace Ȝ. The French also tended to substitute -y- for -i-, especially before -u-, -n-, or -m-, or at the end of words, to avoid confusion in reading (see U), might also partly explain this tendency in Middle English. As short for YMCA, etc., by 1915.