Origin of 'Chess Engine'

Let's take a break from the 'Going Mobile' posts, last seen in Going Mobile : CFAA Site, and return to the topic of chess engines, last seen in Label 'Engines' (May 2015). Ever since I wrote that post, I've been wondering about the phrase 'chess engine', as opposed to 'chess computer', 'chess program', or 'chess software'. How long has the term 'chess engine' been in use?

In another recent post, Early Chess on the Web, I mentioned a resource that might let me answer this question: 'The rec.games.chess newsgroups help fill in the blanks.' It didn't take long to locate the earliest mention of 'chess engine' in rec.games.chess:-

I've always figured that I'd use gnuchess for the chess engine -- but I don't have an interface description for gnuchessr. • Need gchessr interface description (October 1991)

Since the term 'gnuchess' isn't exactly a household word, here's what Wikipedia has to say:-

GNU Chess is a free software chess engine which plays a full game of chess against a human being or other computer program. The goal of GNU Chess is to serve as a basis for research. It has been used in numerous research contexts. [...] The first version of GNU Chess was written by Stuart Cracraft. Having started in 1984 in collaboration with Richard Stallman prior to his founding of the GNU project, GNU Chess became one of the first parts of GNU. • GNU Chess

It turns out that gnuchess had its own newsgroup, one that was also active in the early days of the Internet. The query Topic search results for engine AND before:1992/01/01 in gnu.chess returns five posts, of which only two are for 'chess engine', the post mentioned above and this one:-

I suggested he turn it in to a chesstool clone, and use gnuchessn as the chess engine. • Chesstool interface (May 1991)

From this I can say with some confidence that the term 'chess engine', as opposed to 'chess interface', dates back to 1991. As for 'chesstool', I have no idea what it means, and will save that topic for another time.