hydrolleyEtymology* Blend of hydrogen + trolley coined at the Fourth International Hydrail Conference, Valencia, Spain, in 2008hydrolley means any streetcar or tram vehicle using on-board hydrogen as a source of energy to power the motors. Lexicurio rates it Rare gem — a strength score of 82 out of 100.nounAny streetcar or tram vehicle using on-board hydrogen as a source of energy to power the motors.