derny
A motorized bicycle for paced cycling events such as keirin.
Of course, a familiar sight in a velodrome is the derny, with its characteristic engine sound. Before the cyclists come onto the track, the derny riders perform a few laps to warm up their engines.
Where it comes from
Borrowed from French derny, named after the French manufacturer of the original derny bicycle, Roger Derny et Fils.
Adapted from the Wiktionary entry derny (CC BY-SA 4.0).