Synonyms of 'instantaneous'
immediateDictionary, prompt, instant
Death was not instantaneous.
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You use direct to describe an experience, activity, or system which only involves the people, actions, or things that are necessary to make it happen.
He has direct experience of the process.
My immediate reaction was one of digust.
Thesaurus for instantaneous from the Collins English Thesaurus
Something that is instantaneous happens immediately and very quickly.