An ass is technically the same thing as the donkey, but in common use, 'donkey' seems to be used more often for the domestic strains, and 'ass' for the wild species currently. 'Ass" was used more often in older literature, too.

They mean the same thing. 'Ass' is not used much (at least by Americans) because it can be confused with ass as a part of the body - the buttocks (屁股). Used that way, the word is offensive to many people so it is generally not used in order to avoid offending anybody by mistake.

Try to use Donkey. Ass and Don key have the same meaning as follows : a long-eared, slow, patient, sure-footed domesticated mammal, Equus asinus, related to the horse, used chiefly as a beast of burden. ********************************************************************************** Donkey and ass can both be used as follows : a stupid, foolish, or stubborn person. ********************************************************************************** However, only ASS can be used in this meaning (Vulgar): 1. the buttocks. 2. the rectum. **********************************************************************************