Definition of "mountainous"

mountainous

/ˈmaʊn.tɪn.əs/

adjective
comparative more mountainous, superlative most mountainous
1. Having many mountains; characterized by mountains; of the nature of a mountain; rough (terrain); rocky.
  Quotations
  [Water vapour bubbles] hit againſt the ſides of the more eminent and Mountainous Places, of the Globe, and by this Concuſſion are condenſed, and thus become heavier than the Air they ſvvom in, and ſo gleet dovvn the rocky Caverns of theſe Mountains, […]
  1705, George Cheyne, “Of the Existence of a Deity”, in Philosophical Principles of Natural Religion: […], London: […] George Strahan […], § XXIX, page 184
2. Resembling a mountain, especially in size; huge; towering.
  Quotations
  But the added size did not give them an advantage this time. Not when Kanter and Adams, two mountainous players, could match the Knicks’ girth with their own.
  2016 November 28, Mike Vorkunov, “Despite Flash of Rose’s Prime, Knicks Are Dazed by Westbrook and Thunder”, in The New York Times‎
3. (figurative, of a problem or task) Very difficult.
4. (obsolete) Inhabiting mountains; hence, barbarous.