Definition of have a plum in one's mouth in English:

have a plum in one's mouth

phrase

British
  • Have an accent thought typical of the English upper classes.

    ‘an affable dilettante with a plum in his mouth’
    • ‘His idea of inhabiting the character is to talk like he has a plum in his mouth.’
    • ‘‘He got stuck in on the rugby field but even then he spoke as though he had a plum in his mouth,’ recalled Robin.’
    • ‘He reckons he speaks with a plum in his mouth.’
    • ‘The way Miss Long speaks which sounds like she has a plum in her mouth I find absolutely fascinating and when she rolls those eyes of hers brilliant.’