glacier:A large accumulation or river of ice in a high mountain valley, formed by the gradual descent and consolidation of the snow that falls on the higher ground. The resulting mass is often many miles in length, and continues to move slowly downward until it reaches a point where the temperature is high enough to melt the ice as fast as it descends.——Oxford English Dictionary

glacier:a large mass of ice which moves slowly down a mountain valley.——Longman Dictionary of Contemporary English  @en