To “play gooseberry” is a British idiom meaning to be an unwanted third person when two other people, particularly two who are having a romantic relationship, wish to be alone together (Oxford English Dictionary).
The origin of the gooseberry role is a matter of speculation. One theory is that the third person is a chaperone, who plays with or counts gooseberries while the two lovers carry on.
It is not known whether the "goose" portion of the word comes from a lost association with geese as birds or if it derives from either Old French groseille (berries) or Dutch kruisbes (gooseberry).
The American equivalent is to be a "third wheel".
This is also related to the proverb "Two is company, three is a crowd".
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