Definition of non-return in English:

non-return

adjective

British
  • Permitting the flow of air or liquid in one direction only.

    ‘a nonreturn valve’
    • ‘Its only moving parts are a spring-loaded ‘clack’ valve and a non-return flap valve.’
    • ‘Self-sealing crashworthy fuel tanks have explosion suppression and non-return valves.’
    • ‘If it is taking in air it means that the non-return valve is leaking and needs to be replaced.’
    • ‘Watering outdoor plants isn't likely to be a high priority on these wet days but if you do use a hose for the garden, or to wash the car, remember to fit a non-return valve on the tap to prevent back-flow.’
    • ‘A non-return flap is usually fitted to prevent cold air coming in.’

Pronunciation:

non-return

/ˌnänrəˈtərn/