What is 坊 in 朝寝坊する? I always thought that in was a bit weird. At least in Chinese, means "small factory". Thus I assumed it was a pun about "went to work at the morning sleeping factory" though it seems a bit far-fetched. How come it is not just or even ?

in Japanese is fairly uncommon on its own, but it means something like 'kid' or 'boy' most of the time (originally it was 'monk', and it's shifted a bit semantically). is a somewhat playful term for someone who has trouble getting up in the morning, and as a verb means 'sleep late' or 'oversleep'. is basically the same thing.

's modern Chinese meaning is probably the result of it being used as the simplification of an unrelated character, but I could be wrong.