See glacier in Webster's New World College Dictionary
noun
a large mass of ice and snow that forms in areas where the rate of snowfall constantly exceeds the rate at which the snow melts: it moves slowly outward from the center of accumulation or down a mountain until it melts or breaks away
See glacier in American Heritage Dictionary 4
(glāˈshər)
noun
A huge mass of ice slowly flowing over a land mass, formed from compacted snow in an area where snow accumulation exceeds melting and sublimation.