window box
From Longman Dictionary of Contemporary EnglishRelated topics: Gardening, Householdwindow boxˈwindow box noun [countable] DLGDHa long narrow box in which you can grow plants outside your windowExamples from the Corpuswindow box• If you don't have one, get a window box or hanging basket.• There, perched on the window box with her nose glued to the other side of the glass, was Violet.