The crossword solution for the term 'MULE'S DADDY' is ASS, which is an acronym for a domesticated animal of the same name. An ASS, or donkey, is a hoofed mammal that is related to horses and zebras. It is typically used as a working animal, such as for carrying heavy loads or pulling carts. The term 'MULE's daddy' is a reference to the male parent of a MULE, which is a hybrid animal created by breeding a male donkey with a female horse.