Definition of "bugaboo"

At any rate you must all be ready now to judge the religious life by its results exclusively, and I shall assume that the bugaboo of morbid origin will scandalize your piety no more.

1902, William James, “Lecture I”, in The Varieties of Religious Experience: A Study in Human Nature […] , New York, N.Y.; London: Longmans, Green, and Co. […]

Rather, our discussion of inference is devoted mostly to the finite-sample bugaboos that should bother practitioners.

2009, Joshua D. Angrist, Jörg-Steffen Pischke, Mostly Harmless Econometrics: An Empiricist's Companion, Princeton University Press, page xiii