code: public void removeKeyword(String keyword) {
          if (!taxonomy.concepts.containsKey(keyword)) {
              throw new IllegalArgumentException(String.format("Concept %s does not exist.", keyword));
          }
  
          taxonomy.concepts.remove(keyword);
          if (synset != null) {
              synset.remove(keyword);
          }
      }
docs: Remove a keyword from the concept synset.