Chlorophyll
WordNet
noun
(1) Any of a group of green pigments found in photosynthetic organisms; there are four naturally occurring forms
WiktionaryText
Noun
- Any of a group of green pigments that are found in the chloroplasts of plants and in other photosynthetic organisms such as cyanobacteria
Trivia
Chlorophyll was the winning word at the 20th Scripps National Spelling Bee. http://en.wikipedia.org/wiki/Scripps_National_Spelling_Bee