General:
* Beginner: This is a good synonym if you are emphasizing someone's lack of experience.
* Novice: Similar to "beginner," this implies someone is new to something.
* Dabbler: This suggests someone who is not very serious about their hobby.
* Nonprofessional: This is a neutral synonym that simply means someone is not paid for their work.
* Unprofessional: This implies a lack of skill or expertise, and may be negative.
More specific:
* Hobbyist: This is a good synonym if you are talking about someone who does something for enjoyment.
* Layperson: This is used for someone who is not an expert in a particular field.
* Unpaid: This is a synonym if you are emphasizing the lack of compensation.
The best synonym to use will depend on the specific situation and the intended meaning.