1. occurring, done, or completed in an instant: an instantaneous response.
  2. existing at or pertaining to a particular instant: the instantaneous position of the rocket.


  1. occurring with almost no delay; immediate
  2. happening or completed within a momentinstantaneous death
  3. maths
    1. occurring at or associated with a particular instant
    2. equal to the limit of the average value of a given variable as the time interval over which the variable is considered approaches zeroinstantaneous velocity

1640s (implied in instantaneously), formed in English from Medieval Latin *instantaneus, from instantem (see instant (n.)) on model of spontaneous. Related: Instantaneousness.

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