accumulate (v.)

1520s, "to heap up" (transitive), from Latin accumulatus, past participle of accumulare "to heap up, amass," from ad "to," here perhaps emphatic (see ad-), + cumulare "heap up," from cumulus "heap" (from suffixed form of PIE root *keue- "to swell"). From 1759 in intransitive sense of "grow in size or number." Related: Accumulated; accumulating.