English to English

noun (n)

• (physics and chemistry) the simplest structural unit of an element or compound(noun.substance)

  source: wordnet30
• (nontechnical usage) a tiny piece of anything(noun.substance)

  Synonym:
  atom, corpuscle, mote, particle, speck
  

  source: wordnet30
• One of the very small invisible particles of which all matter is supposed to consist.(noun)

  source: webster1913