A place housing a variety of animals primarily for display to the public.
Sometimes used metaphorically to describe a wild and crazy situation.
History & Etymology
Obviously the word zoo comes from Zoology, but let’s look a little deeper.
Prior to the 1800s establishments like zoos that allow the public access to viewing animals wasn’t really necessary. Prior to the industrial revolution most people lived further from the cities and closer to the wilderness. As the industrial revolution was winding down, around the 1840s, many people had moved into the cities, and had very few interactions with animals of any kind other than pets.
It was around this time that the Zoological Society of London was putting together a little project they called a Zoological Garden. It originally opened for the scientific community in 1828, but its popularity, and the addition of the animals from the menagerie of the Tower of London, made it obvious that they needed to open to the public and that’s what they did in 1847.
Of course the name Zoological Garden was a bit of a mouthful, and I’m fairly certain a lot of the clientele from the public were children, it didn’t take long for the that name to be shortened to simply zoo. With the popularization of other similar attractions such as the Clifton Zoo, and the song ”Walking in the Zoo" This shorthand for Zoological Garden quickly became the standard terminology for this kind of attraction.
This is a great example of how difficult it is to control language. I am certain that the Zoological Society of London would have preferred that the name of their establishment remain “the Gardens of the Zoological Society of London” but alas when words are given to a free people they become their own thing.