instantaneous

UK: /ˌɪnstənˈteɪniəs/

US: /ˌɪnstənˈteɪniəs/

US: (in′stən tā′nē əs)

WordReference Random House Learner's Dictionary of American English © 2026

in•stan•ta•ne•ous /ˌɪnstənˈteɪniəs/   adj. 

1. occurring or completed in an instant;
   immediate:
   an instantaneous response.

in•stan•ta•ne•ous•ly, adv.: 

The image of the explosion was transmitted instantaneously all over the world.

WordReference Random House Unabridged Dictionary of American English © 2026

in•stan•ta•ne•ous  (in′stən tā′nē əs), adj. 

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.

• Medieval Latin instantāneus. See instant, -an, -eous
• 1645–55;

in•stan•ta•ne•i•ty  (in stan′tn ē′i tē, in′stən tə nē′-), in′stan•ta′ne•ous•ness, n.  in′stan•ta′ne•ous•ly, adv. 
Synonyms

• 1. immediate, sudden, abrupt.

Collins Concise English Dictionary © HarperCollins Publishers::

instantaneous / ˌɪnstənˈteɪnɪəs/ adjective

1. occurring with almost no delay; immediate
2. happening or completed within a moment: instantaneous death

ˌinstanˈtaneously adverb

ˌinstanˈtaneousness, instantaneity / ɪnˌstæntəˈniːɪtɪ/ noun