surname and masc. given name, from Gaelic donn "brown, dark" (see dun (adj.)) + ceann "head." Or else from Old Irish, Old Gaelic Donnchad "brown warrior."
familiar term for an ass, 1785, also donky, donkie, originally slang or dialectal, of uncertain origin. Perhaps a diminutive from dun "dull gray-brown" (from Middle English donned, past participle of donnen "to lose color, fade, from Old English dunnian). Compare Dunning, name of a (dun) horse (mid-14c.), and see dun (adj.). The form perhaps was influenced by monkey.
Or perhaps it is from a familiar form of the proper name Duncan applied to an animal (compare dobbin). The older English word was ass (n.1). Applied to stupid, obstinate, or wrong-headed persons by 1840. In mechanics, used of small or supplementary apparatus from mid-19c. (donkey-engine, donkey-pump, etc.). Short form donk is by 1916.
"pertaining to atoms," 1670s as a philosophical term (see atomistic); scientific sense dates from 1811, from atom + -ic. Atomic number is from 1821; atomic mass is from 1848. Atomic energy first recorded 1906 in modern sense (as intra-atomic energy from 1903).
March, 1903, was an historic date for chemistry. It is, also, as we shall show, a date to which, in all probability, the men of the future will often refer as the veritable beginning of the larger powers and energies that they will control. It was in March, 1903, that Curie and Laborde announced the heat-emitting power of radium. [Robert Kennedy Duncan, "The New Knowledge," 1906]
Atomic bomb first recorded 1914 in writings of H.G. Wells ("The World Set Free"), who thought of it as a bomb "that would continue to explode indefinitely."
When you can drop just one atomic bomb and wipe out Paris or Berlin, war will have become monstrous and impossible. [S. Strunsky, Yale Review, January 1917]
Atomic Age is from 1945. Atomical "concerned with atoms," also "very minute," is from 1640s. Atomic clock is from 1938.