code: def add_synonym(self, syn):
          
          n = self.node(syn.class_id)
          if 'meta' not in n:
              n['meta'] = {}
          meta = n['meta']
          if 'synonyms' not in meta:
              meta['synonyms'] = []
          meta['synonyms'].append(syn.as_dict())
docs: Adds a synonym for a node