\Thill\, n. [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.
[root]236. Cf. {Fill} a thill, {Deal} a plank.]
1. One of the two long pieces of wood, extending before a
   vehicle, between which a horse is hitched; a shaft.
2. (Mining) The floor of a coal mine. --Raymond.
{Thill coupling}, a device for connecting the thill of a
   vehicle to the axle.