From Longman Dictionary of Contemporary Englishtricycletri‧cy‧cle /ˈtraɪsɪkəl/ noun [countable] 
TTBa bicycle with three wheels, especially for young children
TTBa bicycle with three wheels, especially for young childrenExamples from the Corpus
tricycle• As he opened the door and looked out he thought he heard the squeak of a tricycle.• It seemed to withstand the onslaught of bicycles, tricycles and roller skates with scarcely a scratch to show.• Both little girls were silent, pale and tight-lipped while Liz tended to the gash, caused by a falling tricycle.• I pushed Janir home on his tricycle, made him dinner and put him to bed.• There are no tricycles in the hallway, no small sandals behind the doors.• One young boy exercised by riding a red tricycle around the wards.• They came to steal a Big Wheel tricycle.• And there's a special appearance from the Dean of Hereford cathedral, complete with tricycle.Origin tricycle (1900-2000) French tri- + Greek kyklos “circle, wheel” 