Chlorophyll

Webster's Dictionary

(n.) Literally, leaf green; a green granular matter formed in the cells of the leaves (and other parts exposed to light) of plants, to which they owe their green color, and through which all ordinary assimilation of plant food takes place. Similar chlorophyll granules have been found in the tissues of the lower animals.

The Nuttall Encyclopedia

The green colouring matter in plants, especially the leaves; due to the presence and action of light.