accumulation (n.) Look up accumulation at Dictionary.com
late 15c., "that which is heaped up, an accumulated mass," from Latin accumulationem (nominative accumulatio) "a heaping up," noun of action from past participle stem of accumulare "to heap up, amass," from ad- "in addition" (see ad-) + cumulare "heap up," from cumulus "heap" (see cumulus). Meaning "act of heaping up" is from c. 1600.