Sentence:  Throughout the 1500s, the populace roiled over a constellation of grievances of which the forest emerged as a <WSD>key</WSD> focal point. The popular late Middle Ages fictional character Robin Hood, dressed in green to symbolize the forest, dodged fines for forest offenses and stole from the rich to give to the poor. But his appeal was painfully real and embodied the struggle over wood. 
Meaning of the word marked with <WSD> tags:  Important, salient.