WordWeb Online

1. Collect in one place, esp. growing to a large number or quantity
   "Journals are amassing in my office";
   - accumulate, cumulate, conglomerate, pile up, gather
    
2. Get or gather together (a large number of something)
   "She is amassing a lot of data for her thesis";
   - roll up, collect, accumulate, pile up, compile, hoard

Derived forms: amassing, amasses, amassed

Type of: hive away, increase, lay in, put in, salt away, stack away, stash away, store

Encyclopedia: Amass