Definition of undercrackers in English:

undercrackers

plural noun

British
informal
  • Men's underpants.

    • ‘It's not much good having a go at someone for being uncultured when you're stood there in your undercrackers, really.’
    • ‘It seems that the vast majority of men's undercrackers are quite dull and boring - lots of dull solid colours, and the occasional tartan or stripe - but nothing even approaching a mild version of jazzy.’

Pronunciation:

undercrackers

/ˈʌndəkrakəz/