c. 1200, from Old French montaigne (Modern French montagne), from Vulgar Latin *montanea "mountain, mountain region," noun use of fem. of *montaneus "of a mountain, mountainous," from Latin montanus "mountainous, of mountains," from mons (genitive montis) "mountain" (from PIE root *men- (2) "to project").
Until 18c., applied to a fairly low elevation if it was prominent (such as Sussex Downs, the hills around Paris). As an adjective from late 14c. Mountain dew "raw and inferior whiskey" is attested by 1839; earlier a type of Scotch whiskey (1816); Jamieson's 1825 "Supplement" to his Scottish dictionary defines it specifically as "A cant term for Highland whisky that has paid no duty." Mountain-climber recorded from 1839; mountain-climbing from 1836.