| atoll |
a ring-shaped island or reef that surrounds a lagoon. |
| atom |
an invisible component of any element, consisting of protons, neutrons, and electrons, once considered the smallest possible unit of matter. [2 definitions] |
| atom bomb |
see "atomic bomb." |
| atomic |
of or relating to atoms or to the use of atoms in creating energy. [3 definitions] |
| atomic age |
(often cap.) the period in history characterized by the development and use of atomic energy in the generation of electrical power and for immensely destructive weapons. |
| atomic bomb |
an extremely destructive weapon, the explosive power of which derives from the immense amount of energy suddenly released when the nuclei of uranium 235 or plutonium atoms are split; atom bomb. |
| atomic clock |
an extremely accurate timekeeping device regulated by the reliably constant frequency at which atoms of certain highly reactive substances absorb or emit electromagnetic radiation. |
| atomic cocktail |
(informal) a dose of a liquid, taken orally, that contains a radioactive substance used in the diagnosis or treatment of cancer. |
| atomic energy |
the energy that is released by an atom in nuclear reactions such as fission or fusion. [2 definitions] |
| atomicity |
the number of atoms in a molecule. [2 definitions] |
| atomic mass unit |
a unit equal to one twelfth of the mass of an atom of the most abundant kind of carbon, equal to 1.6605 times 1024 gram. |
| atomic number |
the number of protons or positive electrical charges in the nucleus of one atom of a given element. [2 definitions] |
| atomic pile |
see "nuclear reactor." |
| atomic theory |
any of several theories concerning the structure, properties, or behavior of atoms. [2 definitions] |
| atomic weight |
the average weight of one atom of a given element, expressed in atomic mass units. |
| atomism |
a theory that all matter is composed of small, indivisible particles called atoms, which in modern form is called atomic theory. [2 definitions] |
| atomistic |
of or relating to atoms or atomism. [2 definitions] |
| atomize |
to divide into atoms. [3 definitions] |
| atomizer |
a device that converts a liquid, esp. a medicine or perfume, into a spray. |
| atom smasher |
see "accelerator." |
| atonal |
in music, composed without a fixed key or scale. |