An entry on "Stocks" in a 1773 edition of Encyclopedia Britannica (http://books.google.com/books?id=Ow8UAAAAQAAJ&pg=PA629
) mentions what it considers "improper" and "erroneous" usage of the term "stocks" to refer to bonds or other financial instruments.
"stocks are a share in a company's funds, bought without any condition of having the principal returned"
"India bonds indeed (by some persons, tho' erroneously
, denominated stock) are to be excepted."
"By the word stock
was originally meant a particular sum of money contributed to the establishing of fund to enable a company to carry on a certain trade by means of which the person became partner in the trade and received a share of profit made thereby, in proportion to the money employed"
"But this term has been extended further, though improperly
, to signify any sum of money which has been lent to the government, on condition of receiving certain interest till the money is repaid, and which makes a part of national debt."
I also found an entry in "The Merchant's Magazine" from 1712 (http://books.google.com/books?id=Ma82AAAAMAAJ&pg=PA208
) describing a stock broker, which uses the terms stock and shares in basically their modern meaning:
"Brokers of Stock
are such as buy and sell Shares in Joint Stock for any one that shall desire them; as if I am minded to buy two Shares in the East-India
Stock, I speak to a Broker if he knows of any to sell, he enquires and finds one that will sell two Shares, which the Broker buyeth for me at the Price currant on the Exchange, and when the same are transferred to me In the Company's Book, I pay for them."
Also, I don't think the "Stock Market" referred exclusively to trading UK government bonds at any point. In fact shares of "Joint Stock" companies were traded in London (starting in the 1500s - East-India Company was founded in 1600) long before the first government bonds were ever created (with the establishment of Bank of England in 1694) I believe the original meaning of Stock and Shares referred to the modern concept of equity, and bonds (both government and corporate) came later, but were then also traded on the same Stock Exchanges as equity shares, and the term 'Stock" became more ambiguous with time.