mountainous
adj.adj. having many mountains or being very large like a mountain. You use this to describe a landscape or a huge pile of something.
adj. characterised by the presence of many mountains; also used figuratively to describe something of immense size or height. Often used attributively before a noun.
The hikers explored the mountainous region.
The country's mountainous terrain makes it difficult to build high-speed railways between the major cities.
Despite the mountainous challenges facing the new administration, the president expressed confidence that the proposed economic reforms would eventually stabilize the national currency.
From mountain + -ous after Middle French montagneux, from Late Latin montāniōsus, from montānia, from Latin montem (“mountain”).
Typically precedes the noun it modifies; when used figuratively, it emphasizes overwhelming scale.