1) A fault, in a mining context.
This word occurs in colliery accounts when the miners had encountered a problem. The OED has two meanings in such contexts
as a fault, or as ‘a mass of rock or earthy matter enclosed within a lode or vein’. A definition is quoted from a work on mining in Cornwall, that is: ‘dead ground in a lode which widens like a horse’s back from the spine’, and an example is given from 1778. The same analogy is apparent in the use of ‘mare’, which is dealt with under that heading, and possibly in the alternative ‘rider’, found in the Craven Glossary. It is defined there as the intrusion into the vein of ‘heterogeneous matter’. The Yorkshire evidence is rather earlier: 1718 to John Wilkinson gate up the horse, Farnley
1783 a coalpit … set upon a horse or fault that runs across part of the estate, Batley. An undated plan of a Beeston colliery has the title Coals and Direction of the Horse, and there is a reference in 1787, also in Beeston, to the north side of the dike or horse.
2) Part of a grinding wheel.
John Birley was an Attercliffe yeoman who made his will in 1545, leaving to Hugh Swan his bellowes, sithes, hamors and tonges with all the things belonging to the smithy and also the horse whele and harnes. This is a very early reference to a wheel equipped with ‘horsing’, designed to enable him to carry out his own grinding. Similarly, in 1554, James Tailior of Heeley granted the whele before the doore to his son Thomas, who was to fynd his parte of horse and harness for the same.