funny money

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Informal Counterfeit currency.
2. n. Informal Money from an obscure or questionable source.
3. n. Informal Currency that has been artificially inflated or deflated for social or political reasons.

Wiktionary

1. n. idiomatic Money gained in a devious or sneaky manner.
2. n. informal, US A highly inflated currency.
3. n. slang, US Bills of any foreign currency or of counterfeit origin.
4. n. slang Play money.