# lunacy

/ˈɫunəsi/ (US) · /lˈuːnəsi/ (UK)

Source: https://englishreference.com/word/lunacy
Updated: 2026-08-08

## Senses

### 2. mental illness

noun · CEFR C2 · Archaic

an old-fashioned word for being mentally ill.

For teachers: an archaic term for insanity or mental derangement, historically associated with the phases of the moon.

- In the old story, the character was locked away because of his supposed lunacy.
- The 19th-century legal documents categorized various behavioral disorders under the broad and imprecise heading of lunacy.

Teaching tip: This sense is archaic and potentially offensive; modern speakers use 'mental illness' or specific clinical terms instead.

## Examples

- The plan to build a bridge over the river was pure lunacy.
- The sudden decision to cancel the entire season was seen as a complete lunacy by the fans and the board.
- The historian argued that the war was a tragic lunacy, driven by a combination of personal grudges and a failure to understand the geopolitical landscape.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.