A name given to half pennies of base metal and somewhat thinner though larger than the regal issues. The name is said to be derived from the fact that they were brought from Genoa by the galleymen who traded in London, and a spot known as the Galley Key (? quay), in Lower Thames Street, near Tower Hill, was the locality from which they were circulated.
They were declared fraudulent by Acts of Henry IV and Henry V, but continued to be brought into England until their circulation was finally prohibited by statute in 1519.
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)