"Tributary glaciers" refers to smaller glaciers that flow into a larger glacier, similar to how smaller streams flow into a larger river. Full definition
Mass loss of Larsen B tributary glaciers (Antarctic Peninsula) unabated since 2002. (antarcticglaciers.org)
The data revealed widespread enhanced flow, with tributary glaciers reaching deep into the ice - sheet's interior. (antarcticglaciers.org)
Ice - shelf structure seems to be important, with sutures between tributary glaciers resulting in weaker areas of thinner ice, which are susceptible to rifting [11]. (antarcticglaciers.org)