English Words Starting With O

• opioid epidemic

  nounC1
  /ˌəʊ.pi.ɔɪd ˈep.ɪ.dem.ɪk/A widespread public health crisis involving a sharp increase in the misuse of, addiction to, and deaths from opioid drugs, both prescription painkillers and illicit substances like heroin and synthetic opioids (e.g., fentanyl).
• opisthobranch

  adjectivenounVery Low
  /əˈpɪsθə(ʊ)braŋk/A member of the Opisthobranchia, a large group of marine gastropod molluscs (sea slugs and related forms) characterised by having the gills behind the heart.
• opisthodomos

  nounVery Low (C2+ Specialist)
  /ˌɒpɪsˈθɒdəmɒs/A rear room or porch at the back of a classical temple, often used as a treasury.
• opisthograph

  nounC2
  /ɒˈpɪsθəˌɡrɑːf/A manuscript or tablet that has writing on both sides.
• opisthosoma

  nounVery Low
  /ˌɒpɪsθə(ʊ)ˈsəʊmə/The posterior part of the body in arachnids and some other arthropods, distinct from the prosoma (cephalothorax).
• opium

  nounC1
  /ˈəʊ.pi.əm/A highly addictive narcotic drug obtained from the unripe seed pods of the opium poppy (Papaver somniferum).
• opium den

  nounLow Frequency
  /ˈəʊ.pi.əm ˈden/A place, often a room or establishment, where people gather to smoke opium.
• opium poppy

  nounC1
  /ˈəʊ.pi.əm ˈpɒp.i/A species of flowering plant (Papaver somniferum) cultivated as the primary source of opium and its derivatives, including morphine and codeine.
• opium war

  nounC1/C2
  /ˈəʊ.pi.əm wɔː/A historical conflict in the 19th century between China and Western powers (primarily Britain), sparked by China's attempts to suppress the opium trade.
• opium wars

  plural-nounC1
  /ˈəʊpɪəm wɔːz/Two conflicts in the mid-19th century between China and Western powers (primarily Britain and France) over trade, diplomacy, and China's sovereignty.
• opiumism

  nounVery Low / Obsolete
  /ˈəʊ.pi.ə.mɪ.zəm/The condition of being addicted to opium.
• opole

  nounVery low (specialist historical/geographical term)
  /ɒˈpɒleɪ/A historical territorial and administrative unit in early medieval Poland, specifically in the Silesian region.
• oporto

  nounLow
  /əʊˈpɔː.təʊ/A major city and seaport in northwest Portugal, located on the Douro River estuary.
• opossum

  nounC1
  /əˈpɒsəm/a small to medium-sized marsupial mammal with a pointed snout and prehensile tail, native to the Americas, known for its habit of feigning death when threatened.
• opossum block

  nounVery Low
  /əˈpɒsəm blɒk/A small, pre-assembled unit, often a cage or enclosure, specifically designed for housing and transporting opossums.
• opossum shrimp

  nounLow
  /əˈpɒsəm ʃrɪmp/A small, shrimp-like crustacean of the order Mysida, often transparent and possessing a brood pouch.
• opotherapy

  nounExtremely Rare / Obsolete (C2+)
  /ˌɒpə(ʊ)ˈθɛrəpi/A historical or very specialist medical treatment involving the administration of animal glandular extracts or organ preparations.
• oppenheim

  nounLow
  /ˈɒpənhaɪm/A German and Jewish surname of Ashkenazi origin, often referring to people or families bearing that name.
• oppenheimer

  nounLow to medium (proper noun; frequency spikes significantly in historical/scientific discourse and surrounding media events like film releases).
  /ˈɒpənˌhaɪmə/A proper noun most commonly referring to J. Robert Oppenheimer (1904–1967), the American theoretical physicist who led the Manhattan Project during World War II, responsible for the development of the first nuclear weapons.
• oppidan

  adjectivenounVery low
  /ˈɒpɪd(ə)n/A student at certain British boarding schools (especially Eton College) who lives in town rather than in school boarding houses.

Showing 1501–1520 of 3187 words.