Y

yard (yd) [1]: a traditional unit of distance equal to 3 feet or 36 inches. The yard is the fundamental unit of distance in the English customary system. The word comes from a Saxon word gird or giard meaning a stick, and the Saxon kings are believed to have kept official yardsticks at Winchester as early as the middle of the 10th century. As for the length of the yard, there is a traditional tale that Henry I decreed in the 12th century that the yard should be the distance from the tip of his nose to the tip of his outstretched finger, thus defining the yard as exactly 1/2 fathom. By the late 13th century it appears that the yard was within a millimeter of its present length. Today one yard is officially equal to exactly 91.44 centimeters or 0.9144 meter; this definition was established in Britain by the Weights and Measures Act of 1963 and has now been accepted in the United States as well. See Length
yard (yd) [2]: the yard is traditionally used as a unit of area for materials sold in standard rolls, such as cloth, carpet, linoleum, fencing, and so on. In each case, one yard represents an area one yard long and as wide as the roll width. See bolt.
yard (yd) [3]: a cubic yard (about 764.555 liters). Bulk commodities like sand or topsoil are often sold by the "yard."
yard of ale: a traditional Scottish measure of volume. A yard of ale is roughly 2.5 pints (1.4 liters) served in a slender, yard-tall glass.
year (a or y or yr) [1]: a unit of time, defined to be the period of time required for the Earth to make one revolution around the Sun. To be more precise, the year we use in ordinary life is the interval between two arrivals of the Sun at the Tropic of Capricorn, marking the winter solstice. Astronomers call this unit the tropical year. There are 365.242 199 days in a tropical year, the Earth-Moon System travels around the Sun, Every 365.242199 days, or; 365 days 5 hours 48 minutes 45.97 seconds or, to be even more precise, 31,556,925.974.7 seconds. See Time
year (a or y or yr) [2]: a traditional unit of time usually equal to 365 or 366 days. We need a whole number of days for the calendar year used in ordinary life. Ancient astronomers knew that the year is approximately 365 days long, and we now know the correct figure is about 365.2422 days. If we use 365 as the number of days in every calendar year, the extra 0.2422 day adds up quickly and causes large errors in predicting the seasons. To solve this problem, the Roman emperor Julius Caesar decreed in 46 BC that the calendar year should have 365 days generally, but that every fourth year should have an extra, or 366th, day. The longer year is called a leap year. In this Julian calendar, four years equal exactly 1461 days, so the average Julian year is exactly 365.25 days. See Time; This was a big step toward accuracy in the calendar, but the Julian year is too long by 0.0078 day, or 11.232 minutes. By the time of the Renaissance, these 11-minute errors had accumulated to a total error of about 10 days, so that the spring equinox was occurring near March 11 instead of March 21. In 1582, Pope Gregory XIII decreed that 10 days should be dropped from the calendar: the day after 1582 October 4 was October 15. To reduce future errors, the pope further decreed that years divisible by 100 are not leap years unless they are also divisible by 400. Thus 2000 and 2400 are leap years, but 2100, 2200, and 2300 are not.; With this adjustment, there are exactly 146 097 days in every 400 years, and the average Gregorian year is exactly 365.2425 days. The Gregorian year is still too long, but only by 0.000 301 2 yr, or about 26 seconds. It takes more than 3200 years for this error to accumulate to 1 day, so the calendar year and the tropical year are in good enough agreement to last us a long time.
yocto- (y-): a metric prefix denoting 10^-24 (one septillionth). Adopted by the CGPM in 1990, the prefix is derived from the Latin octo and Greek okto, meaning 8, because this is the eighth prefix (n = 8 in 10^-3n) in the SI system of metric prefixes. The y was added arbitrarily to provide a non-confusing letter for abbreviations.
yoke: another name for a pair. The yoke is used in describing teams of animals, especially oxen, used to pull plows or wagons.
yotta- (Y-): a metric prefix denoting 10²⁴ (one septillion). The prefix was coined to parallel the prefix yocto-.