Instantaneously is a related term of promptly.
As adverbs the difference between instantaneously and promptly
is that instantaneously is without any delay; in an instantaneous manner while promptly is in prompt manner; both soon and quickly.
instantaneously
English
Adverb
(-)
Without any delay; in an instantaneous manner.
Synonyms
* (without delay) immediately, in a flash, instantly, outright, right now
promptly
English
Adverb
(
en adverb)
In prompt manner; both soon and quickly.
*
- the ducklings nestled down inside it and promptly fell asleep.