Noun pile up has 1 sense
  1. pileup - multiple collisions of vehicles
    --1 is a kind of collision
,Verb pile up has 3 senses
  1. accumulate, cumulate, conglomerate, pile up, gather, amass - collect or gather; "Journals are accumulating in my office"; "The work keeps piling up"
    --1 is one way to increase
    Sample sentences:
    Something ----s
    Something is ----ing PP
  2. pile up, heap up, stack up - arrange into piles or stacks; "She piled up her books in my living room"
    --2 is one way to gather, garner, collect, pull together
    Sample sentences:
    Something ----s
    Something is ----ing PP
    Somebody ----s something
    Somebody ----s something PP
  3. roll up, collect, accumulate, pile up, amass, compile, hoard - 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"
    --3 is one way to store, hive away, lay in, put in, salt away, stack away, stash away
    Sample sentence:
    They pile up the money in the closet
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