Word
lunacy
Phoneticslu·na·cy, stress on the first syllable
US/ˈɫunəsi/
UK/lˈuːnəsi/
Definitions
01extreme foolishness
B2 · Upper Intermediate Uncountable noun
n. behavior that is very stupid, dangerous, or makes no sense.
n. extreme foolishness or irrationality in behavior or policy. Often used for emphasis in critical contexts.
“It would be absolute lunacy to drive across the mountains during a blizzard.”
“The board's decision to invest the entire pension fund into a single volatile startup was dismissed by analysts as pure financial lunacy.”
02mental illness
C2 · Proficiency Uncountable noun Medicine Archaic · Technical
n. an old-fashioned word for being mentally ill.
n. a term formerly used in legal and medical contexts to denote insanity, believed to be influenced by the moon.
“In the nineteenth century, many people were locked away in hospitals for what was then called lunacy.”
“The historical archives contain harrowing accounts of patients committed to the asylum under the broad and ill-defined legal category of lunacy.”
Usage
In modern medical and legal contexts, this term has been replaced by specific clinical diagnoses.
Teaching tip
Learners should avoid using this sense in modern clinical or social contexts as it is considered dated and potentially offensive; use 'mental illness' instead.
Antonyms
Etymology
From lunatic + -cy.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Word family
NOUN
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.C1 AdvancedIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.7.0–8.0TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 5.0–5.595–113TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.945–990
- Frequency
- Occasional
- Level
- C1 · Advanced
- Updated
- アルファベット
- 読み方の一覧 →
QR code
englishreference.com/q/lunacy