One of the mysteries of the English language finally explained.
Synonyms of mountainous in English:
mountainous
See definition of mountainous
adjective
1‘a mountainous region’
SYNONYMS
hilly, craggy, rocky, alpine, high, steep, precipitous
upland, highland
ANTONYMS
flat
2‘mountainous waves’
SYNONYMS
huge, enormous, gigantic, massive, very big, very large, great, giant, colossal, mammoth, vast, immense, tremendous, mighty, formidable, staggering, monumental, Herculean, epic, prodigious, monstrous, titanic, towering, king-sized, king-size, gargantuan, substantial
informal mega, monster, whopping, whopping great, thumping, thumping great, humongous, jumbo, hulking, astronomical, astronomic
British informal whacking, whacking great, ginormous
ANTONYMS
tiny, minute