Wordorigins.org

Hendrickson, R. and Facts on File Inc. (1987). The Facts on File encyclopedia of word and phrase origins. New York, N.Y., Facts on File.

This is perhaps the worst book on word origins available on the market. It is rife with errors that even a minimally competent researcher would have avoided. To be fair, there is a newer third edition of this work available that appears to be improved, although I have not looked comprehensively at this newer edition.