Chestnut
A chestnut was a type of Earth tree that bore nuts.

In the song "I'll Be Seeing You", the two lovers would meet at chestnut trees in an unnamed city. When they became separated, this was one of the places one of the lovers would visit, reminiscing about the relationship. ()

The term "chestnut" could also refer to an old work of literature. In 2375, The Doctor referred to the song "Oh My Darling, Clementine" as an old chestnut. ()

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Earth plants
Slang