Definition of "cyanobacterium"

cyanobacterium

noun
plural cyanobacteria
1. (biology) Any of very many photosynthetic prokaryotic microorganisms, of phylum Cyanobacteria, once known as blue-green algae.
  Quotations
  At some point in the first billion years of life, cyanobacteria, or blue-green algae, learned to tap into a freely available resource – the hydrogen that exists in spectacular abundance in water.
  2003, Bill Bryson, A Short History of Nearly Everything, BCA, published 2003, page 262
  Photosynthesis was established some billion years ago by ancient bacterial precursors of modern cyanobacteria.
  2011, Terence Allen, Graham Cowling, The Cell: A Very Short Introduction, Oxford, page 91