Definition of Dry January in US English:

Dry January

noun

British
  • January as a month in which one refrains from drinking any alcohol as a personal challenge.

    ‘I had a crack at Dry January but crumbled on day two’
    ‘having done Dry January for the last two years, I know full well the benefits of abstaining from alcohol’

Origin

Early 21st century: Dry January is promoted by the charity Alcohol Concern, which has trademarked the term for various goods and services.