From Longman Dictionary of Contemporary Englishinstantaneousin‧stan‧ta‧ne‧ous /ˌɪnstənˈteɪniəs◂/ adjective IMMEDIATELYhappening immediately modern methods of instantaneous communication —instantaneously adverb
Examples from the Corpus
instantaneous• Death from a massive heart attack was almost instantaneous.• Fortunately for him, his death was instantaneous. 