| 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. |
| at once |
at the same time. [2 definitions] |
| atone |
to make reparation for a sin, crime, error, or the like (usu. fol. by "for"). [2 definitions] |
| at one |
in a state of harmony or accord. |
| atonement |
the act of atoning; reparation. [3 definitions] |
| at one's elbow |
close by. |
| at one's fingertips |
readily available. |