/at"euhm/ , n.
1. Physics.
a. the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.
b. an atom with one of the electrons replaced by some other particle: muonic atom; kaonic atom.
2. Energy. this component as the source of nuclear energy.
3. a hypothetical particle of matter so minute as to admit of no division.
4. anything extremely small; a minute quantity.
[ 1350-1400; ME attomos, athomus atomus átomos, n. use of átomos undivided, equiv. to a- A- 6 + tomós divided, verbid of témnein to cut ]
Syn. 4. shred, speck, scintilla, iota, jot, whit.