Sentence:  Suddenly from a lumpy tussock of old grass some twenty yards in front of them, with black-tipped ears erect and long hinder limbs throwing it forward, started a hare. It bolted for a <WSD>thicket</WSD> of alders. 
Meaning of the word marked with <WSD> tags:  A dense, but generally small, growth of shrubs, bushes or small trees; a copse.