n [ U ]
a ceremony that takes place every summer on the River Thames , in which groups of people in boats mark swans (= large white water birds with long necks) to show who owns them. Most swans in Britain belong to the queen, but in the 15th century a few groups of swans on the Thames were given to two of the City of London’s livery companies . The young birds descended from these groups are marked each year to distinguish them from the royal swans.