Learner's definition of MCCOY
the real McCoy
something or someone that is real or genuine
something or someone that is not a copy or imitation
Is that a fake gun, or is it the real McCoy? [=is it a real gun?]
These diamonds look like the real McCoy, but they could be fake.
To help her play the role of a lawyer, the actress studied with the real McCoy. [=with an actual lawyer]
Maybe he's the McCoy, and maybe he's not.