Definition of rainfast in English:

rainfast

adjective

  • (of a chemical spray or other substance) not able to be washed away by rain.

    • ‘This product is cheaper, has a better safety profile, controls both types of rhizomes and is rainfast after 2 hours.’
    • ‘Allow at least six hours for the glyphosate products to become rainfast.’
    • ‘This spray is longer lasting than the copper sprays used on tomatoes, and it is rainfast.’

Pronunciation:

rainfast

/ˈreɪnfɑːst/