one of the flat green parts of a plant that are joined to its stem or branches.——朗文当代大辞典

A flattened structure of a higher plant, typically green and blade-like, that is attached to a stem directly or via a stalk, and in most plants is the chief organ of photosynthesis and transpiration; one of the parts of a plant which collectively constitute its foliage.——牛津当代大辞典  @en