English Words Starting With H

• hydrogen chloride

  nounLow (Specialist)
  /ˈhaɪ.drə.dʒən ˈklɔː.raɪd/A colourless, pungent gas with the chemical formula HCl.
• hydrogen cyanide

  nounLow (Specialist/Tech)
  /ˈhaɪdrədʒən ˈsaɪənaɪd/A highly poisonous chemical compound with the formula HCN, existing as a colorless gas or liquid.
• hydrogen electrode

  nounTechnical/Low
  /ˈhaɪdrədʒən ɪˈlɛktrəʊd/A reference electrode based on the standard hydrogen electrode potential, where hydrogen gas at 1 atmosphere pressure is bubbled over a platinum electrode immersed in a solution with hydrogen ion activity of 1.
• hydrogen embrittlement

  nounC2
  /ˈhaɪdrədʒən ɪmˈbrɪtlmənt/A degradation process where metals become brittle and crack due to the absorption and diffusion of hydrogen.
• hydrogen fluoride

  nounC1
  /ˈhaɪdrədʒən ˈflʊəraɪd/A chemical compound composed of hydrogen and fluorine atoms (HF), existing as a colorless gas or liquid.
• hydrogen iodide

  nounLow (Technical/Scientific)
  /ˈhaɪ.drə.dʒən ˈaɪ.ə.daɪd/A colorless, corrosive gas (HI) that is a binary inorganic compound of hydrogen and iodine, dissolving in water to form a strong acid.
• hydrogen ion

  nountechnical/chemical
  /ˈhaɪ.drə.dʒən ˈaɪ.ɒn/A positively charged ion (H⁺) formed when a hydrogen atom loses its electron; the fundamental acidic species in aqueous chemistry.
• hydrogen peroxide

  nounB2
  /ˈhaɪdrədʒən pəˈrɒksaɪd/A chemical compound (H₂O₂), a clear liquid with strong oxidizing properties, commonly used as a disinfectant, bleach, or propellant.
• hydrogen sulfide

  nounLow
  /ˈhaɪdrədʒən ˈsʌlfaɪd/A colourless, toxic, flammable gas with the characteristic foul odour of rotten eggs, with the chemical formula H₂S.
• hydrogen sulphate

  nounLow
  /ˈhaɪ.drə.dʒən ˈsʌl.feɪt/A chemical compound with the formula HSO₄⁻; the anion formed when one proton is removed from sulphuric acid (H₂SO₄). Also refers to salts containing this anion.
• hydrogen sulphide

  nounB2/C1
  /ˈhaɪ.drə.dʒən ˈsʌl.faɪd/A colourless, toxic gas with a strong, unpleasant smell of rotten eggs, with the chemical formula H₂S.
• hydrogen sulphite

  nounLow
  /ˈhaɪdrədʒən ˈsʌlfaɪt/A salt or ester of sulphurous acid containing the anion HSO₃⁻.
• hydrogen tartrate

  nounC1
  /ˈhaɪdrədʒən ˈtɑːtreɪt/A salt or ester of tartaric acid containing one replaceable hydrogen atom.
• hydrogenate

  verbverb-transitiveC2
  /ˈhaɪ.drə.dʒə.neɪt/To chemically combine with hydrogen.
• hydrogenize

  verbverb-transitiveVery low / Technical
  /ˈhaɪdrədʒənaɪz/To cause to combine with hydrogen; to treat with hydrogen.
• hydrogenolysis

  nounLow
  /ˌhʌɪdrədʒ(ə)ˈnɒlɪsɪs/A chemical reaction involving the cleavage of a chemical bond by hydrogen.
• hydrogeology

  nounLow (Specialized Technical Term)
  /ˌhaɪ.drəʊ.dʒiˈɒl.ə.dʒi/The branch of geology concerned with the distribution, movement, and quality of water within the Earth's crust, particularly in aquifers.
• hydrograph

  nounC1
  /ˈhaɪ.drə.ɡrɑːf/A graph showing the flow rate or water level of a river or body of water over a period of time.
• hydrography

  nounC1/C2
  /haɪˈdrɒɡ.rə.fi/The scientific description and mapping of bodies of water (especially oceans, seas, coasts, and lakes), including their physical features, depths, currents, tides, and navigational hazards.
• hydroid

  adjectivenounLow/Very Low
  /ˈhaɪdrɔɪd/Any member of the class Hydrozoa, a group of small, primarily marine animals, many of which are colonial and have a two-stage life cycle (polyp and medusa).

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