tough cookie (tʌf ˈkʊkɪ). ( 1 informal) if you describe someone as a tough cookie, you mean that they are unemotional and are not easily hurt by what people say or do ⇒ ■ She really is a tough cookie.efinitions. ( 1 informal) if you describe someone as a tough cookie, you mean that they are unemotional and are not easily hurt by what people say or do ⇒ ■ She really is a tough cookie.