WordNet (r) 3.0 (2006):

piggy bank
    n 1: a child's coin bank (often shaped like a pig) [syn: piggy
         bank, penny bank]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "piggy bank":
   Fort Knox, bank, bursary, cash register, cashbox, chest, coffer,
   coin box, depository, exchequer, fisc, gold depository, locker,
   money chest, penny bank, pork barrel, public crib, public till,
   public treasury, public trough, repository, safe, safe-deposit box,
   storehouse, strong room, strongbox, subtreasury, till,
   treasure-house, treasury, vault