During a report on the radio last week about a fire at Bradford's Drummond Mills, the reporter commented on the fact that the word shoddy was still visible in big letters on the wall of the factory, indicating the building's longevity. Shoddy is not a reference to the quality of the goods manufactured there, but is a type of material. Shoddy, according to the OED, is a "woollen yarn obtained by tearing to shreds refuse woollen rags, which, with the addition of some new wool, is made into a kind of cloth". The word thus came to mean something worthless trying to pass for something superior. The origin of the word is unknown, although it is possible that it is a derivative of shoad, which refers to fragments of tin, lead or copper ore. The OED mentions this as a possibility, as it is also possible that the original meaning of the word shoddy was inferior coal, or the smaller stones in a quarry.
A similar material is mungo, defined in the OED as "fibres produced by shredding old woven or felted material; inferior cloth made from such fibres". This comes from the original meaning of mung, namely 'a mingling, a mixture, a confusion'.
A similar word history occurred with the modern-day words sleazy and tawdry. The OED mentions sleasie-lawn, a fine cloth. In the 17th and 18th centuries Silesia,a region that straddles Poland and the Czech Republic, was renowned for the manufacture of fine linen, and unscrupulous merchants from elsewhere would sell cheap material, pretending it was Silesian. This fraudulent trade was so widespread that the term 'Silesia cloth' became synonymous with shoddiness (see this old post of mine). Tawdry was originally short for tawdry lace, tawdry being named after St Audrey (see this old post). The women of East Anglia would once buy tawdry lace adornments and jewellery at fairs held in honour of their patron saint. In time cheap and tacky versions of the necklaces were produced and sold at a lower price, hence today's meaning of the word tawdry.