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 indicate how many. One, three, and fifteen are cardinal numbers.
compound number a quantity expressed in two different but related units of measure, as dollars and cents or pounds and ounces.
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 made up of a whole number and a fraction.
natural number any positive integer.
number one (informal) oneself or one's own interests. [2 definitions]
number plate the British word for a small metal sign on a car, truck, or other vehicle indicating that the vehicle is legal to drive on public roads. Number plate has the same meaning as license plate.
number-cruncher (informal) a person, machine, program or the like that performs a great many complicated numerical calculations.
octane number a number that designates the antiknock properties of a gasoline, based on the percentage of isooctane in it; octane rating.
ordinal number any number that indicates a position in a numbered order. "First," "third," "fifteenth," and "thousandth" are ordinal numbers.
perfect number a positive integer that is equal to the sum of its divisors, including one but excluding itself.
Personal Identification Number an identification number entered on a keypad to gain remote electronic access to one's bank account or other financial accounts.
phone number a short form of telephone number.
prime number a number that can be evenly divided only by itself or by one. Two and eleven are prime numbers.