A folding door or gate made of two panels hinged together, or any structure consisting of two leaf-like parts joined together.
From 'double' plus 'leaf,' where 'leaf' in this technical sense refers to a movable panel or section of a door (from Old English 'leaf'). This usage dates back to architectural terminology.
Architects borrowed the word 'leaf' from actual plant leaves because doors and gates have the same hinged, fold-open quality—when you swing open a doubleleaf door, it moves just like leaves opening to sunlight.
Complete word intelligence in one call. Free tier — 50 lookups/day.