The OED, Second Edition, does include _espresso_ and _expresso_, the latter being a variant of the former. It correctly derives it from Italian _caffe espresso_. [Accents left off here.] Whoever claimed it derives the term from a would-be Italian _caffe e

Dave Bogie’s classic document – a must-read for every coffee fiend

Third in the trio – the original Caffeine FAQ, has some overlap with the coffee FAQ

mmmmmm….