Main definitions of rat pack in US English:

: rat pack1rat pack2

rat pack1

noun

informal
  • A group of five friends and co-performers prominent in the entertainment industries of Hollywood and Las Vegas in the 1950s and 1960s. The group (Frank Sinatra, Dean Martin, Sammy Davis, Jr., Joey Bishop, and Peter Lawford) made several movies together, including Ocean's Eleven (1960).

Main definitions of rat pack in US English:

: rat pack1rat pack2

rat pack2

noun

British
informal
  • A ration pack issued by the army to men on duty away from base camp.

    • ‘None was forthcoming, so I made a deal with the devil and concocted a cup of chocolate consisting of the heat-whitened end of a Flake, most of a waxen bar of choc from an Army rat pack, and instant coffee.’
    • ‘We're taking out about three boxes of human waste and about 10 bags of burnable rubbish, a bag of recyclable rubbish, quite a lot of unused rat packs, and a couple of polar pyramid tents.’
    • ‘Yesterday I only used four packets, so toady I used the other three and mixed the sauce plus chilli sauce and the beans from today's rat pack.’