The term 'expressed by word of mouth' can be summarized by two crossword solutions: ORAL (4 letters) and PAROL (5 letters). ORAL is defined as spoken rather than written, while PAROL is defined as a spoken agreement or promise. Both terms refer to the act of expressing something verbally, without the use of written language. This is often used to communicate information quickly and efficiently, as well as to make agreements that are not legally binding.