(n.) a spiral staircase
A word dating back to the fifteenth century in English, a turngree, or turngrece, is a spiral staircase.
The ‘turn’ part here is self-explanatory, given the twisting arrangement of steps in a spiral staircase—but what about ‘gree’? Well, it is a Middle English word for a flight of steps or stairs, recorded in English texts since the mid 1300s. It derives from its older French equivalent, gré, which is in turn descended at length from a Latin word for a step, gradum. Via the same root, turngree is related to words like gradual, retrograde, digress and—coincidentally ending up spelled precisely the same—degree.
The alternative spelling with a C here, turngrece, comes from the old plural form of gree, but both spellings were used substantively (i.e. as a collective singular noun) to refer to a single flight or set of steps. They remained in use in the language until the early seventeenth century, when their use steadily began to dwindle, leaving them clinging on in only a handful of northern dialects, including Scots.