Sentence:  Then a cluster is grown by letting each empty <WSD>neighbour</WSD> of an already occupied cluster site decide once and for all, whether it is occupied or empty. One needs to keep and to update a perimeter list of empty <WSD>neighbours</WSD>. 
Meaning of the word marked with <WSD> tags:  A person living on adjacent or nearby land; a person situated adjacently or nearby; anything (of the same type of thing as the subject) in an adjacent or nearby position.