A language is a living organism that constantly changes. Words often take on another meaning over time.

Let me give you an example:

HOTHOUSE

Originally this word meant a heated building, usually made of glass, used to grow plants.

This is what it still means today, but the word is now also used figuratively referring to a place or situation with intense activity, usually to promote the development of somebody or something.

New York in the 1940s was a hothouse of artists and intellectuals.
For decades the palace was a hothouse of intrigue.

Hothouse can also be used as a verb meaning to train a child intensively in sport, music, academic work, etc. This often has a negative connotation.

Some newspaper articles imply that women are hothousing their children when they are simply trying to do the best they can for their families.

While walking to school a father is checking his daughter's knowledge to see if she has done her homework
Are we hothousing our children?

So here we see a change in meaning from something good – promoting the growth of plants – to something negative – disapproval of the way some parents train their children.

A word related to hothouse is hotbed, which originally also had to do with the growing of plants. When used figuratively, hotbed especially in British English usually refers to an unwanted or unpleasant activity.

The village had turned into a hotbed of disease.

Can you think of other English words that have taken on a completely new and different meaning?