greenhouse

the compound 'greenhouse' is a transparent formation from middle english, directly combining the old english words for the color 'green' and a 'house' or building. the term originally described a structure, often a small outbuilding or a section of a manor, where tender plants were kept during winter; its walls were sometimes literally painted green, but more importantly, it housed living 'green' plants. by the 17th century, as glass became more affordable, the defining feature became the glazed walls and roof that allowed sunlight in to nurture plants, solidifying the modern meaning. the later, abstract sense relating to the 'greenhouse effect' (mid-20th century) is a metaphorical extension, comparing the atmosphere's heat-trapping function to that of a plant-growing glasshouse.

Structure: green (color) + house (building) green (old english 'grēne', meaning the color green; functional role: descriptive modifier). house (old english 'hūs', meaning a dwelling or building; functional role: head noun).