Green and orange make brown. Per Color Matters, green and orange are both secondary colors, meaning that they are made by mixing two primary colors. Mixing any two secondary colors yields a brown shade, from muddy brown to olive brown.
The exact shade of brown that green and orange yield depends on the shades of green and orange. Light colors yield a light, yellowish brown while dark colors yield a darker, more olive shade of brown. Mixing green or orange with a primary color may yield a tertiary color, but mixing the two secondary colors never yields anything but brown, regardless of hue or brightness.