tricycle

Concise Oxford English Dictionary © 2008 Oxford University Press:
tricycle/ˈtrʌɪsɪkl/

▶noun a vehicle similar to a bicycle, but having three wheels, two at the back and one at the front.

■ a three-wheeled motor vehicle for a disabled driver.

▶verb (often as noun tricycling) ride on a tricycle.

– derivatives
tricyclist noun.