I. ˈ ̷ ̷ˌ ̷ ̷ noun
( -s )
Etymology: pile (VI) + up
: a collision involving usually several objects and causing damage or injury
was instantly killed in an automobile pileup — Springfield (Massachusetts) Union
II. noun
1. : a jammed tangled mass or pile (as of motor vehicles or people) resulting from collision or accumulation
2. : accumulation