General synonyms:
* Immediate: This is a very common synonym for "instant" and implies that something happens without any delay.
* Prompt: This suggests that something happens quickly and efficiently.
* Rapid: This emphasizes the speed of something.
* Sudden: This implies that something happens unexpectedly or abruptly.
* Quick: This is a general term for something that happens quickly.
* Swift: This is a more formal word for "quick."
More specific synonyms:
* Momentary: This suggests that something lasts for a very short time.
* Fleeting: This suggests that something passes quickly and is gone.
* Blitzkrieg: This suggests a rapid and overwhelming attack or action.
* Flash: This is a very informal word for something that happens very quickly.
* Right away: This implies that something happens immediately.
* On the spot: This suggests that something happens without any preparation.
Other options:
* In a jiffy: This is a casual expression that means "very quickly."
* Right now: This means "at this moment in time."
* Immediately: This is a more formal word for "right away."
The best synonym for "instant" will depend on the specific situation and the meaning you want to convey.