atomic

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Of or relating to an atom or atoms.
• adjective Of or employing nuclear energy.
• adjective Very small; infinitesimal.

from The Century Dictionary.

• In client., existing in the condition of isolated atoms of the same kind; not united into groups to constitute molecules: as, for example, active oxygen at the instant of its separation from hydrogen dioxid.
• Pertaining to atoms; consisting of atoms.
• Extremely minute.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of or pertaining to atoms.
• adjective Extremely minute; tiny.
• adjective see atom bomb in the vocabulary.
• adjective a system which, assuming that atoms are endued with gravity and motion, accounted thus for the origin and formation of all things. This philosophy was first broached by Leucippus, was developed by Democritus, and afterward improved by Epicurus, and hence is sometimes denominated the Epicurean philosophy.
• adjective (Chem.) teaches that chemical combinations take place between the supposed ultimate particles or atoms of bodies, in some simple ratio, as of one to one, two to three, or some other, always expressible in whole numbers.
• adjective (Chem.) the weight of the atom of an element as compared with the weight of the atom of hydrogen, taken as a standard.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective physics, chemistry Of, or relating to atoms
• adjective Of, or employing nuclear energy or processes
• adjective Infinitesimally small
• adjective Unable to be split or made any smaller
• adjective computing Said of an operation that is guaranteed to either complete fully, or not at all.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective of or relating to or comprising atoms
• adjective (weapons) deriving destructive energy from the release of atomic energy
• adjective immeasurably small