code: public static function singularize($word)
      {
          $result = array_search($word, static::$specials, true);
          if ($result !== false) {
              return $result;
          }
          foreach (static::$singulars as $rule => $replacement) {
              if (preg_match($rule, $word)) {
                  return preg_replace($rule, $replacement, $word);
              }
          }
  
          return $word;
      }
docs: Returns the singular of the $word.
  @param string $word the english word to singularize
  @return string Singular noun.