
1) Concurrent 2) Fast 3) Immediate 4) In a jiffy 5) Instant 6) Snap
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https://www.crosswordclues.com/clue/instantaneous

1) Fast 2) Immediate 3) Instant 4) Occurring with no delay
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https://www.crosswordclues.com/clue/instantaneous

• (a.) Done or occurring in an instant, or without any perceptible duration of time; as, the passage of electricity appears to be instantaneous. • (a.) At or during a given instant; as, instantaneous acceleration, velocity, etc.
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http://thinkexist.com/dictionary/meaning/instantaneous/

qualifies the value, at a given instant of time, of a time dependent variable quantity
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http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=191-18-09

1. Done or occurring in an instant, or without any perceptible duration of time; as, the passage of electricity appears to be instantaneous. 'His reason saw With instantaneous view, the truth of things.' (Thomson) ... 2. at or during a given instant; as, instantaneous acceleration, velocity, etc. ... <physics> Instantaneous center of rotation...
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http://www.encyclo.co.uk/local/20973
In`stan·ta'ne·ous adjective [ Confer French
instantané .]
1. Done or occurring in an instant, or without any perceptible duration of time; as, the passage of electricity appears to be
instantaneous . « His reason saw With
instantaneous view, the truth of things....
Found on
http://www.encyclo.co.uk/webster/I/70

This means an event which occurs over a very short (infinitesimal) period of time. It usually refers to speed, i.e. instantaneous speed as opposed to average speed
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http://www.users.zetnet.co.uk/computing/MainPage/SecDepts/Physics/Resources

[
adj] - occurring with no delay
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http://www.webdictionary.co.uk/definition.php?query=instantaneous

in an instant; immediately
Found on
https://sciencetrek.org/sciencetrek/topics/nervous_system/glossary.cfm
instant(a) adjective occurring with no delay; `relief was instantaneous`; `instant gratification`
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https://www.encyclo.co.uk/local/20974

occurring, done, or completed in an instant: an instantaneous response. · existing at or pertaining to a particular instant: the instantaneous position of the rocket.
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https://www.infoplease.com/dictionary/instantaneous
No exact match found.