Why Does ZZZ mean sleep?
Actually, this originated when comic strips before comic strips became very popular and the artists needed something to signify that a character was simply asleep. It soon turned into a very popular representation of sleeping in all sorts of ways, including general idioms: catching some z’s does indeed refer to sleeping, often a nap or lighter sleeping.
The reason zzz came into being is that the comic strip artists just couldn’t represent sleeping with much. Because there is no other way to represent sleeping, the artists came up with onomatopoeia: a sound-word, put simply. The term represents sounds that are spelled out as they sound. Buzz, boom, bang, crash, zip, pow and clang are all onomatopoeias, but are also very real words ‘š depending on their use, they can be actually words, like verbs, or they can represent a sound made, like the buzzing of a bee. That would be the use of ‘buzz, as a noun (actually, technically it’s a gerund, a ‘šing word as a noun). But when I say that the bee went ‘Buzz!,, that is an onomatopoeia. So when a character says ‘zzz, is simply means that they are sleeping, but it is onomatopoeia to represent sleeping.
As the sounds made while sleeping are quite difficult to represent with letters, the artists chose zzz, because it best represents the sound. Capital ZZZs generally mean loud snoring or the like, generally with large, old men, or in an ironic situation by a woman (comic strips are also famous for holding to social norms of gender interpretation). In fact it has made itself into its own meaning ‘š it no longer needs explanation and is generally accepted world wide as a representation of sleeping. The reason it even became what it now is, is almost lost, such as the meaning of the wrong end of the stick. I’ll let you figure that one out.