E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A cart used in mines and on railways. A railway trolly is worked by the hand, which moves a treadle; a coal-mine trolly used to be pushed by trolly-boys; ponies are now generally employed instead of boys. (Welsh, trol, a cart; trolio, to roll or trundle, whence to troll a catchi.e. to sing a catch or round.)