get or gather together; "I am accumulating evidence for the man's unfaithfulness to his wife"; "She is amassing a lot of data for her thesis"; "She rolled up a small fortune"
If you amass something such as money or information, you gradually get a lot of it. How had he amassed his fortune? = accumulate, accrue. if you amass money, knowledge, information etc, you gradually collect a large amount of it (amasser, from masser )