Meaning : A very short time (as the time it takes the eye to blink or the heart to beat).
Example :
If I had the chance I'd do it in a flash.
Synonyms : blink of an eye, flash, heartbeat, jiffy, new york minute, split second, trice, twinkling, wink
Meaning : Occurring with no delay.
Example :
Relief was instantaneous.
Instant gratification.
Synonyms : instantaneous