lunatic

1 of 2

noun

lu·​na·​tic ˈlü-nə-ˌtik 

plural lunatics

1

dated, now offensive : someone affected with a severely disordered state of mind

2

informal : a person who behaves in a wildly foolish, reckless, or uncontrolled manner

lunatic

2 of 2

adjective

1

a

dated, now offensive : affected with a severely disordered state of mind

b

dated, now offensive : providing care to mentally ill people

a lunatic asylum

2

informal : wildly foolish

a lunatic idea

lunatic behavior

Synonyms

Adjective

• foolish
• stupid
• mad
• silly
• absurd
• crazy
• insane
• idiotic
• irrational
• looney
• loony
• fool

Examples of lunatic in a Sentence

Adjective

He hatched a lunatic plot to overthrow the government.

another of his lunatic ideas

Recent Examples on the Web

Noun

But as Plemons so deftly plays him, Teddy doesn’t seem like a lunatic. —Jake Coyle, Boston Herald, 24 Oct. 2025

There were these lunatics in the car. —Literary Hub, 22 Oct. 2025

Adjective

Such a light as this should shine only on murders and public crime, or along the corridors of lunatic asylums. —Rowan Jacobsen, Harpers Magazine, 24 Oct. 2025

In retrospect, Kinetta feels like a dry run for Lanthimos, with all the droll affectation of his later provocations but little of the allegorical power or lunatic comedy that would distinguish them. —A.a. Dowd, Vulture, 24 Oct. 2025

Word History

Etymology

Noun

Middle English lunatik, borrowed from Anglo-French lunatic, borrowed from Late Latin lūnāticus, noun derivative of Latin lūnāticus "suffering from a mental or neurological disorder allegedly affected by the phases of the moon" — more at lunatic entry 2

Adjective

Middle English lunatik "suffering from a recurrent mental or neurological disorder," borrowed from Anglo-French lunatic, borrowed from Latin lūnāticus "suffering from a mental or neurological disorder allegedly affected by the phases of the moon," from lūna "moon" + -āticus, adjective suffix of appurtenance — more at lunar, -age

Note: The word is unattested in classical Latin aside from the legal treatises of Julius Paulus (2nd-3rd centuries a.d.). The derivation was perhaps modeled on fānāticus "inspired by orgiastic rites, fanatic entry 2." Compare Greek (New Testament) selēniázesthai, taken to mean "to suffer from seizures," a derivative of selḗnē "moon."

First Known Use

Noun

14th century, in the meaning defined at sense 1

Adjective

14th century, in the meaning defined at sense 1a

Phrases Containing lunatic

• lunatic fringe

Rhymes for lunatic

• actinic
• agnatic
• bailiwick
• bolshevik
• candlestick
• chloritic
• deontic
• firebrick
• herpetic
• judaic
• orthotic
• politic

Kids Definition

lunatic

1 of 2 adjective

lu·​na·​tic

ˈlü-nə-ˌtik

1

a

: mentally unsound

—used chiefly in the past

b

: designed for the care of mentally ill people

lunatic asylum

—used chiefly in the past

2

: wildly foolish

a lunatic idea

lunatic

2 of 2 noun

: a mentally ill person

—used chiefly in the past

Medical Definition

lunatic

noun

lu·​na·​tic ˈlü-nə-ˌtik 

dated, now offensive : an individual marked by a severely disordered state of mind

Legal Definition

lunatic

noun

lu·​na·​tic

ˈlü-nə-tik

: an insane person

—used especially formerly

lunatic adjective