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. |