1. adjective
a) False, especially of money; intended to deceive or carry appearance of being genuine.
This counterfeit watch looks like the real thing, but it broke a week after I bought it.
b) Inauthentic
2. noun
a) A non-genuine article; a fake.
b) One who counterfeits; a counterfeiter.
3. verb
a) To falsely produce what appears to be official or valid; to produce a forged copy of.
Wikipedia foundation.