English Words Starting With O

• ornithine

  nounC2
  /ˈɔː.nɪ.θiːn/A non-proteinogenic amino acid produced in the urea cycle, essential for the removal of excess nitrogen.
• ornithischian

  adjectivenounC2
  /ˌɔːnɪˈθɪskɪən/A herbivorous dinosaur belonging to the order Ornithischia, characterized by a 'bird-hipped' pelvic structure.
• ornithology

  nounC2
  /ˌɔː.nɪˈθɒl.ə.dʒi/The scientific study of birds.
• ornithomancy

  nounExtremely Rare / Obsolete Technical Term
  /ˈɔː.nɪ.θəʊˌmæn.si/Divination or prophecy by observing the flight patterns, cries, or behaviour of birds.
• ornithophily

  nounC2
  /ˌɔːnɪˈθɒfɪli/Pollination by birds.
• ornithopod

  nounVery Rare
  /ˈɔː.nɪ.θəʊ.pɒd/A type of herbivorous, bipedal dinosaur belonging to the suborder Ornithopoda.
• ornithopter

  nounRare
  /ˌɔːnɪˈθɒptə/A flying machine that achieves lift and propulsion by flapping wings, like a bird or insect.
• ornithorhynchus

  nounC2
  /ˌɔːnɪθəʊˈrɪŋkəs/The scientific genus name for the duck-billed platypus, a semiaquatic, egg-laying mammal native to eastern Australia and Tasmania.
• ornithoscopy

  nounVery rare
  /ˌɔː.nɪˈθɒs.kə.pi/The observation or study of birds.
• ornithosis

  nounVery Low Frequency
  /ˌɔːnɪˈθəʊsɪs/A specific disease found in birds, particularly parrots, that can be transmitted to humans.
• orogen

  nounExtremely Low / Specialist
  /ˈɒr.ə.dʒən/A technical term for a mountain range or a mountain-forming region, primarily used in geology.
• orogeny

  nounLow (C2+ vocabulary, specialized geological term)
  /ɒˈrɒdʒ.ə.ni/The process of mountain formation, especially by folding and faulting of the Earth's crust.
• orographic cloud

  nounVery low frequency, C2 (Proficient user).
  /ˌɒr.əˈɡræf.ɪk klaʊd/A cloud formed when moist air is forced upward over a mountain or other elevated terrain, causing it to cool and condense.
• orographic precipitation

  nounC2
  /ˌɒr.əˈɡræf.ɪk prɪˌsɪp.ɪˈteɪ.ʃən/Rain, snow, or other precipitation caused by moist air being forced upward over mountains.
• orography

  nounC2
  /ɒˈrɒɡrəfi/The branch of geography dealing with mountains and mountain systems; the study of the relief and configuration of mountains.
• oroide

  nounVery rare / Obscure
  /ˈɔːrəʊʌɪd/An alloy, typically of copper, zinc, and tin, resembling gold in appearance; gold-colored metal used in cheap jewelry.
• orometer

  nounVery Low (Highly Technical)
  /ɒˈrɒmɪtə/An instrument for measuring the altitude above sea level, especially in mountainous regions; an altimeter.
• oromo

  nounC1
  /ɒˈrəʊ.məʊ/An ethnic group native to Ethiopia and parts of Kenya, and the Cushitic language spoken by this people.
• oronasal

  adjectivenounVery Low
  /ˌɔːrəʊˈneɪz(ə)l/Relating to or involving both the mouth and the nose.
• orono

  nounVery Low
  /əˈrɒnəʊ/Proper noun referring to the name of a town in Maine, USA, and to a figure from Abenaki mythology.

Showing 2001–2020 of 3187 words.