It took a while for me to find the volume, but almost none to find the reference I was looking for:
ghoul - 1786, in Beckford's "Vathek," from Ar. ghul, an evil spirit that robs graves and feeds on corpses, from ghala "he seized."
I was reminded of ghouls when the soon-to-be five-year-old asked me, "What's a ghoul?" I decided to skip the part about feeding on corpses, but otherwise I think I was pretty accurate in recalling the Arabic origin of the word, and (although I didn't mention it) the English novelist (who actually wrote Vathek in French) who introduced the word into the English language.
I read Vathek several years ago -- William Beckford could probably be the poster boy for the late Edward Said's theory of Orientalism (in fact, scanning the index of Said's work, I find only three passing references to Beckford, and no mention of Vathek). The back cover of my paperback edition of the book -- dated 1983 (Good God, it was quite a few years ago...) tells us that the work
remains one of the strangest eighteenth-century novels and one of the most difficult to classify. Perverse and grotesque comedy alternate with scenes of 'oriental' magnificence and evocative beauty in the story of the ruthless Caliph Vathek's journey to superb damnation among the subterranean treasures of Eblis. Underlying the elegant prose and pervading the whole of the novel is a strong element of self-indulgent personal fantasy on the part of Beckford himself, youthful millionaire, dreamer, and eventually social outcast. Byron, Poe, Mallarme, and Swinburne are but a few of the literary figures who have admired Vathek's imaginative power.
The novel is, by and large, about a pursuit of evil, about a man who sets out on a quest to achieve utter damnation. I enjoyed reading it (and am considering reading it again) because it had the principle virtue of a work of literature: it made me want to know what happened next.