Resembling a mountain in size; huge: mountainous waves. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "mountainous" in a sentence
"Interestingly. while we all cherish the rains and lake replenishment of summer here at Lake Chapala, in mountainous Chiapas and the adjacent flat coastal plain of Tabasco on the Gulf, the rains, while certainly needed and a blessing, bring flooding in the plains and mudslides in the hills that can be devastating."
"If you need water for your car, there are periodic water wells, especially in mountainous areas, but know that the wells are usually on one side of the highway only."
"As often as not in mountainous country you're going to spot that beyond-long-distance elk downhill."