> The first recorded use of the term in print was 1987, in PC Week 8 Sept. 107/2. "Everybody has only one killer application. The secretary has a word processor. The manager has a spreadsheet."
The phrase killer app first appears in print circa 1986 according to Google Ngram Viewer [0].
While a search for just app with Ngram Viewer would contain too much noise, we can reasonably assume that app must have been prevalent in technical jargon before that time, else marketing campaigns would not have used it.
Archive.org isn't reliable for this kind of query.
https://archive.org/search.php?query=%28killer%20app%29%20AN...