Atomic mass unit

n. unit of mass equal to 1/12 the mass of a carbon atom, AMU

The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. It is defined to be one twelfth of the mass of an unbound atom of the carbon-12 nuclide, at rest and in its ground state.1 u = 1/NA gram = 1/ (1000 NA) kg   (where NA is Avogadro's number)1 u ≈ 1.660538782(83) × 10−27 kg ≈ 931.494028(23) MeV/c2See 1 E-27 kg for a list of objects which have a mass of about 1 u.
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Noun
1. unit of mass for expressing masses of atoms or molecules
(hypernym) mass unit

(amu or dalton): The basic unit of mass on an atomic scale. One amu or dalton is one twelfth the mass of a carbon 12 atom (in other words, the mass of a hydrogen atom, ). Therefore, there are amu in one gram (Avogadro number).

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(amu,u) A unit of mass equal to 1/12 the mass of a carbon-12 nucleus, which is 1.660 538 73 × 10-27 kg ± 0.000 000 13 × 10-27 kg [1998 CODATA values ]. Abbreviated as amu or u. Sometimes called the dalton, after John Dalton , architect of the first modern atomic theory .