activity
Pluralactivities
- 1Something that a person or group does, especially for a particular purpose or for enjoyment.
Stretching counts as a light physical activity that improves circulation.
Each task on the schedule was listed as a separate activity.
UsagePeople do or take part in an activity; common pairs are outdoor activities and leisure activities.
- 2The state or quality of being active; busy movement or motion.
Seismic activity increased in the days before the eruption.
The trading floor buzzed with activity as the bell rang.
UsageOften a lot of activity or a flurry of activity; a place is busy with or buzzing with activity.
Similaraction, movement, bustle, motion
Oppositeinactivity, idleness, stillness
- 3The tendency or power of a substance to react chemically with others.
Fluorine shows extremely high activity, reacting with nearly every element.
Chemists compared the activity of each catalyst before the trial.
Similarreactivity
Oppositeinertness
Less common meanings
- 4The number of radioactive decays that occur per unit of time, measured in becquerels or curies.
The activity of the cesium source was recorded in becquerels.
As the isotope decayed, its activity dropped steadily over the month.
Similarradioactivity
Note
Physics turns the word into a rate: how many nuclei in a sample decay each second. One becquerel is one decay per second, and one curie is 3.7 × 10¹⁰ decays per second, so the two units differ enormously in scale. Activity belongs to a source or sample; for a single radionuclide it falls exponentially, halving with each half-life.
Checked 31 Oct 2026 · 5 facts
- Radioactive activity is the rate of nuclear decays in a sample. www2.lbl.gov
- One becquerel equals one decay per second. www2.lbl.gov
- One curie equals 3.7 × 10¹⁰ decays per second, making it vastly larger than one becquerel. www2.lbl.gov
- Activity is a property measured for a radioactive source or sample. www2.lbl.gov
- Exponential decrease applies to an unreplenished population of a single radionuclide. A sample containing multiple radionuclides need not follow one exponential; radioactive daughter activity can initially increase. en.wikipedia.org
- 5The lexical aspect of verbs or predicates that describe change over time but have no natural end point.
Practice
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Origin
The Latin noun activitas passed into Middle French as activité, and English took it from there. In English terms, it is simply active with the suffix -ity added.