lunatic

Etymology

Recorded from the late 13th century.^[1] From Middle English lunatik,^[2][3] borrowed from Old French lunatique,^[2][1] from Late Latin lūnāticus (“moonstruck”),^[1][4] from Latin lūna (“moon”),^[2][5] from the belief that changes of the moon caused intermittent insanity.^[3][6]

Compare Old English monseoc “lunatic”, literally “moon-sick”.^[1] The phrase lunatic fringe was popularized by Theodore Roosevelt in 1913.^[1]

References

1. [1] [2] [3] [4] [5] Harper, Douglas, Online Etymology Dictionary, https://www.etymonline.com
2. [1] [2] [3] The American Heritage Dictionary of the English Language, Boston: Houghton Mifflin
3. [1] [2] Merriam-Webster's Collegiate Dictionary, Springfield, Mass.: Merriam-Webster
4. [1] Random House Webster's Unabridged Dictionary, New York: Random House
5. [1] Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
6. [1] Wiktionary, the free dictionary, https://en.wiktionary.org