from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. An onslaught; an assault.
  • n. A beginning; a start: the onset of a cold.
  • n. Linguistics The part of a syllable that precedes the nucleus. In the word nucleus (no͞oˈklē-əs), the onset of the first syllable is (n), the onset of the second syllable is (kl), and the last syllable has no onset.

from Wiktionary, Creative Commons Attribution/Share-Alike License

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

from the GNU version of the Collaborative International Dictionary of English

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

from The Century Dictionary and Cyclopedia

  • To assault; begin.
  • n. 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.
  • n. Start; beginning; initial step or stage; outset.
  • n. An attack of any kind: as, the impetuous onset of grief.
  • n. Something set on or added by way of ornament.

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

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


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


  • 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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  • 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.


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

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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 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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  • 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