piggy bank vs money box

piggy bank and money box both are nouns.

Word	Noun	Adjective	Verb	Adverb
piggy bank	Yes	No	No	No
money box	Yes	No	No	No

As nouns, money box is a hypernym of piggy bank; that is, money box is a word with a broader meaning than piggy bank:

piggy bank: a child's coin bank (often shaped like a pig)
money box: a container (usually with a slot in the top) for keeping money at home

Other hypernyms of piggy bank include bank, coin bank, savings bank.

piggy bank (noun)	money box (noun)
a child's coin bank (often shaped like a pig)	a strongbox for holding cash
	a container (usually with a slot in the top) for keeping money at home