1) Any large roughly shaped piece of wood, from which the term for wooden shoes eventually developed.
We are likely to be most familiar with this word in the sense of ‘wooden shoe’, that is the traditional north-country clog which was strengthened with iron or brass at the heels and edges, and had irons on the thick wooden sole. However, the evidence for this usage is comparatively late and may date with certainty only from the seventeenth century: 1692 gave William Goodall [a coal miner] to pay for his cloges 6d
1696-7 For ... yroning his Cloggs, Conistone
1723 a pair of clogs, Whitley
1755 one pair of Leather Clogs, East Ardsley. In an inventory submitted to the magistrates in 1731, Timothy Eyre of Austerfield listed a paire of leather cloages among the possessions he had lost in a disastrous fire. It is true that clogs are referred to from the late fourteenth century: 1390 patens et clogges, York but the connection with pattens means that these are likely to have been wooden-soled overshoes, of the type worn by women to protect their feet from wet or dirt. Both Walpole and Jane Austen mention women’s clogs in this sense as late as the eighteenth century. It was no doubt the wooden sole of the clog that was responsible for its name. Much earlier, certainly from the fourteenth century, the more general use of the word was to any substantial and roughly shaped piece of wood, as in 'a Clog of an Oke' employed c.1400 as a weapon. One chopin clogg in a Pudsey inventory in 1633 was probably used for chopping firewood, and a clogg in Huddersfield market place in 1716 was a butcher’s stall. Similar clogs of wood are mentioned frequently. The fabric rolls for York Minster in 1418 list ix magnis clogges, and in 1553 a Birstall dyer left all the timber at his door and three clogges in the Workhouse Croft to his son. The Yule clog was the heavy piece of wood burnt on the fire at Christmas, in Scotland in particular: the similarity between this term and Yule log is of interest, for both clog and log are of uncertain etymology and it is tempting to think that they may share a common history.In a less-usual context Bradford tenants were ordered in 1663 to scour the ditches … from the Clogg of Wood wherein the wimble hole is: a wimble was a boring tool, probably an auger. It is possible therefore that this prominent piece of timber had served an earlier purpose, for clogs of wood were sometimes attached to grazing animals, in order to impede their movement and prevent them from straying. They were even attached to human beings, by a cord or chain I imagine, so clogs of this kind would have needed a hole bored through them. Smaller bits of wood could be used more positively, tied to an object so that it could not be lost. In 1562, it was said that 'Euery key hath a clog', a practice that has not died out.Examples of clog as a verb are not uncommon. In 1694, a workman called William Priestley was paid 4d for clogging the bells of Almondbury church. I am uncertain what the precise meaning of this phrase was, but presumably it involved holding or restraining the movement of the bells with large pieces of wood. To ‘clog up’ the works would eventually be a widely-used phrase. In the sense of ‘encumbrance’ the word also had figurative uses, most comically in 1577, when a wife was described as 'a grieuous clog to her husband'. An enigmatic entry in Haworth parish register in 1733 gives a list of marriages at Bradford and by clog and shoe in Lancashire. Although this could be interpreted as some unusual local custom it may simply mean that the married couple had walked over into Lancashire to be married. Haworth was, after all, right on the county boundary.