It is short for the obsolete word "hockamore", which is an alteration of "Hochheimer", derived from the name of the town of Hochheim am Main in Germany.
The term seems to have been in use in the 17th century, initially for white wines from the middle Rhine, but in the 18th century it came to be used for any German white wine sold in Britain.
It seems probable that Queen Victoria's visit to Hochheim and its vineyards during harvest time in 1850 contributed to the continued use of the word "hock".
Today "hock" is occasionally seen on bottles of (mostly cheaper) white wine sold in the United Kingdom. In Australia, hock is still known as the main ingredient of an old-fashioned summer drink called "hock, lime, and lemon."