As a Noun:
1. An area of land that is not flat and has many areas with steep sides which are difficult to climb English = mountains.
2. A row of mountains that were formed at the same time in the earth's history. English = mountains, mountain range.
3. An area of land that is not flat. It is uneven and has many areas that are high, but not as high as a mountain. English = hills.
As a Verb or Adjective:
1. To be land which is very high with steep sides which are difficult to climb; to be an area with lots of mountains. English = (be) mountainous, (be) rugged.
2. Of an area of land, to have a lot of hills. English = (be) hilly.