English Words Starting With A

• activated alumina

  nounC1+
  /ˌæk.tɪ.veɪ.tɪd əˈluː.mɪ.nə/A highly porous, granular form of aluminium oxide, used primarily as a desiccant (drying agent) and for adsorbing impurities from liquids and gases.
• activated carbon

  nounLow
  /ˌæk.tɪ.veɪ.tɪd ˈkɑː.bən/A form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions.
• activated mine

  nounLow/Very Low
  /ˈæktɪveɪtɪd maɪn/A mine (explosive device) that has been intentionally armed or triggered, making it ready or dangerous.
• activated sludge

  nounC1/C2 (Very low frequency outside environmental science/engineering contexts)
  /ˌæk.tɪ.veɪ.tɪd ˈslʌdʒ/A semi-solid, biologically active material produced in wastewater treatment, consisting of a concentrated culture of microorganisms used to break down organic pollutants.
• activation analysis

  nounLow
  /ˌæk.tɪˈveɪ.ʃən əˈnæl.ə.sɪs/An analytical technique used in chemistry and physics to determine the concentration of elements in a sample by irradiating it with neutrons or charged particles to make the elements radioactive, then measuring the emitted radiation.
• activation energy

  nounLow-Mid
  /ˌæk.tɪˌveɪ.ʃən ˈen.ə.dʒi/The minimum amount of energy required to initiate a chemical reaction.
• activator

  nounC1
  /ˈæk.tɪ.veɪ.tər/A substance, device, or agent that initiates or increases the activity of something.
• active

  adjectivenounB1
  /ˈæk.tɪv/Engaged in action or movement; functioning or operating.
• active centre

  nounC1+
  /ˈæk.tɪv ˌsen.tə(r)/The specific site within an enzyme or catalyst where the chemical reaction actually occurs.
• active duty

  nounC1-C2
  /ˌæk.tɪv ˈdʒuː.ti/A status of full-time military service, as opposed to reserve or retired status.
• active galaxy

  nounC1-C2 / Specialized
  /ˈæk.tɪv ˈɡæl.ək.si/A galaxy that emits an exceptionally large and energetic amount of radiation from a small central region, due to processes not powered by normal stars.
• active immunity

  nounC1
  /ˈæk.tɪv ɪˈmjuː.nə.ti/The long-term immune protection an individual's own body produces after exposure to a pathogen or a vaccine.
• active layer

  nounLow
  /ˈæk.tɪv ˈleɪ.ə/The top layer of soil or ground that thaws seasonally in permafrost regions.
• active list

  nounC1
  /ˈæk.tɪv lɪst/A current list of items requiring immediate attention or action, typically used in business, military, or technical contexts.
• active mass

  nounC2
  /ˈæktɪv mæs/A specific term in physical chemistry referring to the effective concentration of a substance participating in a reaction.
• active optics

  nounLow
  /ˈæktɪv ˈɒptɪks/A system in telescopes that makes small, continuous adjustments to the shape of the primary mirror to correct for distortions caused by gravity, temperature changes, or wind.
• active reason

  nounVery Low (Specialist)
  /ˈæk.tɪv ˈriː.zən/In Aristotelian and Thomistic philosophy, the aspect of intellect that abstracts universal forms from sensory data, making potential knowledge actual. The immaterial, creative power of the human intellect.
• active safety

  nounC1
  /ˈæk.tɪv ˈseɪf.ti/Safety systems in vehicles that actively work to prevent accidents before they occur, as opposed to passive systems (like airbags) that mitigate injury during an accident.
• active service

  nounC1
  /ˈæk.tɪv ˈsɜː.vɪs/The state of being currently engaged in military duties, especially during wartime or conflict, as a member of the armed forces.
• active shooter

  nounC2 (Very Low Frequency, but crucial in specific registers)
  /ˈæk.tɪv ˈʃuː.tə/A person currently engaged in killing or attempting to kill people with a firearm in a populated area, typically in a random or mass shooting scenario.

Showing 1061–1080 of 8734 words.