# Children's, Intermediate and Advanced Online English Dictionary & Thesaurus

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 A one superior; first-rate; first-class. atomic number the number of protons or positive electrical charges in the nucleus of one atom of a given element. [2 definitions] back number any previous issue of a periodical. call number a series of numbers or numbers and letters used to locate a book in a library. cardinal number any number used to express quantity but not order. (Cf. ordinal number.) compose a number In mathematics education, to add together different place values to make a complete number. For example, to compose the number 231, you would add the three place values that make up this number, a 200, a 30, and a 1. compound number a quantity expressed in two different but related units of measure, as dollars and cents or pounds and ounces. counting number the number one and any number obtained by successively adding one to get the next number. decompose a number In mathematics education, to separate a number into its component place values. For example, to decompose the number 231 you would write "200+30+1". even number a whole number that can be divided exactly by 2. f-number the relative aperture of a camera lens, representing the light it will transmit, which is obtained by dividing the focal length of the lens by the diameter of the aperture. Mach number (sometimes l.c.) the ratio of the speed of an object, or the flow of a fluid, to the speed that sound travels in the environment in which the object, or fluid, is moving; Mach. mass number the total number of neutrons and protons in the nucleus of an atom. mixed number a number consisting of an integer and a fraction, such as two and one half. natural number any positive integer or zero. number line a line that displays real numbers according to their distance in a positive or negative direction from a point defined as zero. number name a name assigned to a quantity, such as one. number one (informal) oneself or one's own interests. [2 definitions] number plate (chiefly British) a metal tag or plate displayed on a motor vehicle and bearing a registration number that qualifies the vehicle as legal to drive on public highways and roads; license plate. number sentence in mathematics education, a simple equation or inequality containing numbers and operators.