From Longman Dictionary of Contemporary Englishwater pistolˈwater ˌpistol noun [countable] British English DHTa toy gun that shoots water
Examples from the Corpus
water pistol• And whoever is in charge of bathtime should watch out ... there's even a water pistol cleverly disguised as a flower.• The kids had been in the car and there was a water pistol on the shelf under the dash.• Lots of events including Tombola and water pistol shooting. 