House Judiciary Chairman Lamar Smith, R-Tenn., noted the word's origin and how mental illness once was believed to be linked to the moon during floor debate Wednesday, The Hill reported.
"The term lunatic derives from the Latin word for moon," Smith said. "Before the modern era, it was used to describe a person who suffers from mental disease because of the belief that lunar cycles have an impact on brain function. But as science and medicine have progressed, society has come to understand mental illness with more clarity."
In the 398-1 vote, the only "no" came from Rep. Louie Gohmert, R-Texas.
In the Senate, where the bill was introduced and passed in May, supporters said U.S. law should reflect a "21st century understanding of mental illness and disease."
The Hill said the word "lunatic" is in sections of U.S. law concerning receivership of estates, and in a section that defines "lunatic" as "every idiot, lunatic, insane person, and person non compos mentis."
The bill now goes to President Obama for consideration.