A flattened structure of a higher plant, typically green and bladelike, that is attached to a stem directly or via a stalk. Leaves are the main organs of photosynthesis and transpiration. A thing that resembles a leaf in being flat and thin, typically something that is one of two or more similar items forming a set or stack. (of a plant, especially a deciduous one in spring) put out new leaves. Turn over (the pages of a book or the papers in a pile), reading them quickly or casually.