The term 'MOUNTAIN Route' can be broken down into two crossword solutions: PASS (4 letters) and MOUNTAIN (8 letters). PASS is a noun that refers to the act of moving past or through something, usually with some difficulty. MOUNTAIN is a noun that refers to a large natural elevation of the earth's surface rising abruptly from the surrounding level. Together, the two words form the phrase 'MOUNTAIN Route, ' which is a route that goes through a MOUNTAIN range.