imitation made to look like something else, usually something more expensive: imitation leather
artificial made to have the same features or do the same job as something else that exists naturally: artificial cream/sweeteners/flavourings
fake made to look like something valuable or important, often in a way that is meant to trick people: fake jewellery or fur
forged made to look exactly like something valuable or important and used illegally to trick people: a forged signature/passport/painting
counterfeit made to look exactly like something valuable or important and used illegally to trick people: used especially for describing illegally produced money: counterfeit currency/traveller’s cheques
phoney (informal) used for describing behaviour and emotions that are not natural or sincere: He didn’t fool anyone with that phoney Italian accent.
bogus (informal) false and used for tricking people or pretending to be somebody you are not: bogus auto partsa bogus repairman
pirate used for describing copies of things such as books or videos that have been made and sold illegally: They were caught selling pirate copies of the album.