mountainous

adjective

moun·​tain·​ous ˈmau̇n-tə-nəs 

ˈmau̇nt-nəs

1

: containing many mountains

2

: resembling a mountain : huge

mountainously adverb

mountainousness noun

Synonyms

• vast
• huge
• gigantic
• enormous
• giant
• massive
• tremendous
• colossal
• mammoth
• immense
• astronomical
• monumental
• astronomic
• monstrous

Examples of mountainous in a Sentence

the seemingly mountainous obstacles he had to overcome while growing up

Recent Examples on the Web

Traffic was not rerouted, and many motorists along the mountainous route had no choice but to remain in their vehicles overnight. —CBS News, 28 June 2025

Indonesia — Halmahera's volcanic rainforests This image features the mountainous Halmahera rainforest in Indonesia, revealing complex topography shaped by volcanic forces. —Daisy Dobrijevic, Space.com, 23 June 2025

The American Kennel Club (AKC) says these dogs were historically bred to guard livestock in mountainous terrain, often working alone and making decisions independently. —Lucy Notarantonio, MSNBC Newsweek, 21 June 2025

The mountainous region along the coast is especially prone to mudslides, with numerous rivers at risk of flooding. —Marlene Lenthang, NBC news, 19 June 2025

Word History

Etymology

Middle English mounteynous, borrowed from Anglo-French muntaignus, from muntaigne, mountaigne mountain + -us -ous

First Known Use

14th century, in the meaning defined at sense 1

Kids Definition

mountainous

adjective

moun·​tain·​ous ˈmau̇nt-ᵊn-əs 

-nəs

1

: having many mountains

2

: resembling a mountain : huge