Is the word modern an adjective?

Yes, "modern" is an adjective. It is used to describe something that is related to the present time or the recent past, or something that is thought of as being characteristic of the present time or the recent past.

For example:

* The modern world is very different from the world of a hundred years ago.

* The modern car is a marvel of engineering.

* The modern office is full of computers and other technology.

In each of these examples, the word "modern" is used to describe something that is characteristic of the present time.