Learner's definition of MOUNTAIN
1 : an area of land that rises very high above the land around it and that is higher than a hill
She watched the sun set behind the mountains.
the Rocky Mountains
He climbed the mountain.
a cabin in the mountains
They both like mountain climbing.
a mountain range/lake
a mountain man [=a man who lives in the mountains]
2 : a very large amount of something
make a mountain out of a molehill