plural lunatics
1
old-fashioned + sometimes offensive
: an insane person
a murderous lunatic
He was raving like a lunatic.
2
informal
: a person who behaves in a very foolish way
I almost got into an accident with some lunatic on the highway.
My boss is a complete lunatic.
He was a lunatic out on the ski slopes. [=he was an extremely daring, reckless, or aggressive skier]
always used before a noun
1
a
old-fashioned + sometimes offensive
: designed for insane people
a lunatic asylum
b
: not sane
a lunatic [=crazy] genius
2
: wildly foolish
He hatched a lunatic plot to overthrow the government.
another of his lunatic ideas
lunatic behavior
a lunatic risk
Cite this Entry
“Lunatic.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/lunatic. Accessed 19 Jun. 2026.
Copy Citation
