Learner's definition of AMATEUR
a person who does something (such as a sport or hobby) for pleasure and not as a job
a person who does something poorly
a person who is not skillful at a job or other activity
The people running that company are a bunch of amateurs.
Only amateurs make this kind of mistake.
He's a mere amateur when it comes to cooking. [=he doesn't know how to cook well]
always used before a noun
an amateur competition [=a contest for amateurs]
They competed at the amateur level.