The Oxford Thesaurus An A-Z Dictionary of Synonyms - accumulationn.

1) collecting, amassing, gathering, piling or aggregation, heaping up: One effect of the strike was the accumulation of rubbish in the streets. 2) growth, increase, build-up: The accumulation of wealth has never proved a valid purpose in life. 3) heap, pile, mass, collection, hoard, store, stockpile, stock, aggregation; assemblage: Our gardener made sure that there was an ample accumulation of compost.