'Chlorophyll a' definitions:

Definition of 'chlorophyll a'

noun

A blue-black plant pigment having a blue-green alcohol solution; found in all higher plants

From: GCIDE

Chlorophyll \Chlo"ro*phyll\, n. [Gr. chlwro`s light green + fy`llon leaf: cf. F. chlorophylle.]
1. (Bot.) 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. [Written also chlorophyl.] [1913 Webster]
2. any of a group of green pigments found in photosynthetic organisms. Chlorophyll a and chlorophyll b are found in higher plants and green algae; chlorophyll c is found in certain types of marine algae. Chemically, it has a porphyrin ring with a magnesium ion bound to the four central nitrogens, and has a phytyl side chain. It is essential for photosynthesis in most plants. {Chlorophyll a} has formula C55H72N4O5Mg.
Syn: chlorophyll. [WordNet 1.5]

From: GCIDE

Chlorophyll \Chlo"ro*phyll\, n. [Gr. chlwro`s light green + fy`llon leaf: cf. F. chlorophylle.]
1. (Bot.) 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. [Written also chlorophyl.] [1913 Webster]
2. any of a group of green pigments found in photosynthetic organisms. Chlorophyll a and chlorophyll b are found in higher plants and green algae; chlorophyll c is found in certain types of marine algae. Chemically, it has a porphyrin ring with a magnesium ion bound to the four central nitrogens, and has a phytyl side chain. It is essential for photosynthesis in most plants. {Chlorophyll a} has formula C55H72N4O5Mg.
Syn: chlorophyll. [WordNet 1.5]