Source : Webster's Revised Unabridged Dictionary (1913)

Greenhead \Green"head\, Greenhood \Green"hood\, n.
   A state of greenness; verdancy. --Chaucer.

Source : WordNet®

greenhood
     n : any of numerous orchids of the genus Pterostylis having
         leaves in a basal rosette and green flowers often striped
         purple or brown or red with the dorsal sepal incurved to
         form a hood [syn: {helmet orchid}]