Definition of thunder-plump in English:

thunder-plump

noun

Northern Irish, Scottish
  • A heavy and sudden shower of rain accompanied by thunder and lightning.

    ‘a very heavy thunder-plump in summer’
    • ‘Another thunderplump cascaded down on him just as he was about to hit his tee shot at the tenth.’
    • ‘Unlike last year's thunder-plump that sent the crowd packing, the humid evening kept the estimated 900 people there until the end.’
    • ‘A thunder-plump caused flooding in the town.’
    • ‘The crop always seems to be drying up and then down comes another thunder-plump.’
    • ‘There comes a thunderplump of rain.’
    • ‘Within 15 minutes a large black cloud looms, which soon produces a thunderplump.’

Origin

Early 19th century: from thunder + plump.