means A bright yellow citrus fruit prized for its sour juice and fragrant peel — and, by extension, anything (especially a car) that turns out to be defective.

from From Old French 'limon' and ultimately Arabic 'laymūn' and Persian 'līmūn', words that traveled the medieval trade routes alongside the fruit itself, which spread west through the Islamic world into the Mediterranean. The 'defective thing' sense is much later American slang, born from the idea of biting into something that leaves a sour taste — by the 20th century it had attached firmly to bad cars.