[L. numerus, number]

1. A total of units.
2. A symbol graphically representing an arithmetical sum.

atomic mass number

A number equal to the sum of all the neutrons and the protons in an atom's nucleus.
SEE: mass number

atomic number

SYMB: Z The number of negatively charged electrons in an uncharged atom, or the number of protons in the nucleus. This number determines the position of elements in the periodic table of elements. It is used to describe isotopes of an element, each of which has a different mass number but the same atomic number.

Avogadro number

SEE: Avogadro, Amedeo

basic reproductive number

ABBR: R0 The number of secondary cases of an infection that spread from a single infected organism to a susceptible community.
SYN: SEE: basic reproductive ratio; SEE: reproductive number of an infectious disease

CAS number

ABBR: CAS RN, CAS # An internationally recognized identifier for each chemical published by the Chemical Abstract Service (CAS). The CAS maintains a database for all known chemicals, including basic properties, toxicity, flammability, and radioactivity.

Drug Enforcement Administration number

SEE: Drug Enforcement Administration number

hardness number

A number on a calibrated scale indicating the relative hardness as determined by a particular system of testing, e.g., Knoop, Mohs, Rockwell, Vickers hardness tests. A steel ball or diamond point is applied with a known variable load for a determined period of time to produce an indentation whose depth or diameter can be measured.

lot number

An identifier assigned to a batch of medications. It facilitates drug manufacturing inventory control and tracing adverse incidents in a batch of contaminated medications.

low-density lipoprotein particle number

SEE: Low-density lipoprotein particle concentration.

mass number

The mass of the atom of a specific isotope relative to the mass of hydrogen. In general, this number is equal to the total of the protons and neutrons in the atomic nucleus of that specific isotope.

OMIM number


reproductive number of an infectious disease

SEE: Basic reproductive number.

saponification number

In analysis of fats, the number of milligrams of potassium hydroxide needed to saponify 1 g of oil or fat.

unique physician identification number

ABBR: UPIN Until it was replaced in 2006, a six-digit code, consisting of numbers and letters, assigned in the U.S. to all health care providers who take care of Medicare patients.
SEE: National Provider Identifier