docs: def _description(self, concept):
          """
          Returns a "description" of a concept,
          as defined in the paper.
  
          The paper describes the description as a string,
          so this is a slight modification where we instead represent
          the definition as a list of tokens.
          """
          if concept not in self.descriptions:
              lemmas = concept.lemma_names()
              gloss = self._gloss(concept)
              glosses = [self._gloss(rel) for rel in self._related(concept)]
              raw_desc = ' '.join(lemmas + [gloss] + glosses)
              desc = [w for w in raw_desc.split() if w not in stops]
              self.descriptions[concept] = desc
          return self.descriptions[concept]