cu·mu·late 
(kymyə-lāt′)
(kymyə-lāt′)v. cu·mu·lat·ed, cu·mu·lat·ing, cu·mu·lates
v.tr.
1. To gather in a heap; accumulate.
2. To combine into one unit; merge.
v.intr.
To become massed.
adj.
Having cumulated or having been cumulated; heaped up or amassed.
[Latin cumulāre, cumulāt-, from cumulus, heap; see keuə- in the Appendix of Indo-European roots.]
cu′mu·lation n.