1. One of the two long pieces of wood, extending before a vehicle, between which a horse is hitched; a shaft.
2. (Science: chemical) The floor of a coal mine. Thill coupling, a device for connecting the thill of a vehicle to the axle.
Origin: OE. Thille, AS. Ille a board, plank, beam, thill; akin to el a plank, D. Deel a plank, floor, G. Diele, OHG. Dili, dilla, Icel. Ilja a plank, planking, a thwart, ili a wainscot, plank; cf. Skr. Tala a level surface. 236. Cf. Fill a thill, Deal a plank.