code: func (v Vocabulary) PartOfSpeech(w string) ([]PartOfSpeech, error) {
    if v.c.WordnikApiKey == "" {
      return []PartOfSpeech{}, Error("WordnikApiKey required.")
    }
  
    contents, err := makeReq(fmt.Sprintf(partOfSpeechApiUrl, w, v.c.WordnikApiKey))
    if err != nil {
      return []PartOfSpeech{}, err
    }
  
    var result []PartOfSpeech
    err = json.Unmarshal(contents, &result)
    if err != nil {
      return []PartOfSpeech{}, err
    }
    return result, nil
  }
docs: // Returns a list of PartOfSpeech structs representing the POS of the given word.