"But the demons of the past," he continued, "were demons of fire and abomination . . . they were enemies we could fight-enemies who inspired fear. Yet Satan is shrewd. As time passed, he cast off his diabolical countenance for a new face . . . the face of pure reason. Transparent and insidious..."
There are no more uses of "insidious" in the book.
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The debt grew insidiously—just a little at a time and always for a good purpose.
Alan Greenspan -- The Age of Turbulence
We’ve grown accustomed to spending more than we earn, but the increasing debt is an insidious problem.