Definition of sub-mountain in US English:

sub-mountain

noun

Geography
  • A peak or upland area that is adjacent to a mountainous region; a peak that is lower than a mountain. Chiefly in plural.

adjective

Geography
  • Attributive Of the nature of a sub-mountain; relating to or characteristic of sub-mountains.

Origin

Late 18th century; earliest use found in William Tooke (bap. 1744, d. 1820), writer and translator. From sub- + mountain.

Pronunciation

sub-mountain

/ˈsʌbˌmaʊntɪn/