from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The beginning or start of something.
  • noun Linguistics The part of a syllable that precedes the nucleus. In the word nucleus (noo͞′klē-əs), the onset of the first syllable is (n), the onset of the second syllable is (kl), and the last syllable has no onset.
  • noun Archaic An attack by military forces; an assault.

from The Century Dictionary.

  • To assault; begin.
  • noun A rushing or setting upon; attack; assault; especially, the assault of an army or body of troops upon an enemy or a fort, or the order for such an assault.
  • noun Start; beginning; initial step or stage; outset.
  • noun An attack of any kind: as, the impetuous onset of grief.
  • noun Something set on or added by way of ornament.

from the GNU version of the Collaborative International Dictionary of English.

  • transitive verb obsolete To assault; to set upon.
  • transitive verb obsolete To set about; to begin.
  • noun A rushing or setting upon; an attack; an assault; a storming; especially, the assault of an army.
  • noun A setting about; a beginning; -- used especially of diseases or pathological symptoms.
  • noun obsolete Anything set on, or added, as an ornament or as a useful appendage.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun A rushing or setting upon; an attack; an assault; a storming; especially, the assault of an army.
  • noun medicine The initial phase of a disease or condition, in which symptoms first become apparent.
  • noun phonology The initial portion of a syllable, preceding the syllable nucleus.
  • noun acoustics The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak.
  • noun obsolete A setting about; a beginning.
  • noun obsolete Anything set on, or added, as an ornament or as a useful appendage.
  • verb obsolete To assault; to set upon.
  • verb obsolete To set about; to begin.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun the beginning or early stages
  • noun (military) an offensive against an enemy (using weapons)


from Wiktionary, Creative Commons Attribution/Share-Alike License

From on- +‎ set. Compare Old English onsettan ("to impose; oppress, bear down").


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  • This is facilitated by a standardized definition of possible yellow fever cases, such as “acute fever followed by jaundice within two weeks of onset of symptoms with bleeding symptoms or with death within three weeks of onset”.

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  • Recognizing that this could be another chronic pain onset, I wanted WCB to cover therapy for a couple of weeks.

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  • The delay in onset of methemoglobinemia in this case, which has been reported only to a limited extent,10 is noteworthy and suggests that a prolonged observation period may be necessary.

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  • The homogenous sand bed represents the first long term onset of Navajo Sandstone in the area.

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  • Premier Michael Misick has called on the Caribbean Community (CARICOM) and a list of international agencies to intervene in the Turks and Caicos Islands to stop what he calls the onset of "modern-day colonialism" in this British-administered territory.

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  • I wonder if today’s rain onset means that the weather has finally decided summer is over?

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  • It's hard enough to call the onset of the recession correctly and arrange the spending so that it happens at precisely the right moment.

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  • The accelerating expansion of the universe that we currently observe, is identified as the onset of inflation.

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  • The right wing beneficiaries of whoring in Iraq will call the onset of hearings a "witch hunt" or retribution.

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  • Chad Crowe Given a set of assumptions, forecasting the peak-oil-point -- defined as the onset of global production decline -- is a relatively trivial problem.

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  • Recruitment information with a link to the survey was placed on three websites where parents and professionals had been observed to describe what seemed to be a sudden or rapid onset of gender dysphoria (4thwavenow, transgender trend, and youthtranscriticalprofessionals), although the specific terminology “rapid onset gender dysphoria” did not appear on these websites until the recruitment information using that term was first posted on the sites.

    Parent reports of adolescents and young adults perceived to show signs of a rapid onset of gender dysphoria Lisa Littman 2023


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  • The outset is when something starts fully formed: This project was doomed from the outset....I promised myself I would work hard from the very outset.

    Onset is something forming: The onset of the disease is slow and painful....I fear the onset of war....The war will be vicious from the outset.

    In terms of usage, it seems onset can be subject or object, whereas outset is always (or at least commonly) prepositional 'from the outset', 'at the outset'.

    September 25, 2010