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1. Multiple collisions of vehicles

1. Collect in one place, esp. growing to a large number or quantity
   "The work keeps piling up";
   - accumulate, cumulate, conglomerate, gather, amass
    
2. Arrange into piles or stacks
   "She piled up her books in my living room";
   - heap up, stack up
    
3. Get or gather together (a large number of something)
   "She piled up a small fortune";
   - roll up, collect, accumulate, amass, compile, hoard

Derived forms: pileups, piles up, piled up, piling up

Type of: collect, collision, garner, gather, hive away, increase, lay in, pull together, put in, salt away, stack away, stash away, store

Encyclopedia: Pileup