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1. Multiple collisions of vehicles

1. Collect or gather, esp. 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: piles up, piled up, pileups, 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