These held, if George remembered correctly, some fifteen thousand volumes-almost everything of importance that had ever been published on the nebulous subjects of magic, psychic research, divining, telepathy, and the whole range of elusive phenomena lumped in the category of paraphysics.
There are no more uses of "nebulous" in the book.
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... all of which fell into the nebulous category of we’re-building-up-God’s-house,
James McBride -- The Color of Water
…hunting on Sunday; war on the increasing tendency of young women to paint themselves and smoke in public; war on drinking whiskey—in this connection at least fifty children per summer went to the altar and swore they would not drink, smoke, or curse until they were twenty-one; war on something so nebulous Jean Louise never could figure out what it was, except there was nothing to swear concerning it; and war among the town’s ladies over who could set the best table for the evangelist.