A person who is interested in a subject or an activity as a hobby(noun)
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Use "hobbyist" in a sentence
"A sign of a dedicated hobbyist is the ability to look at ANYTHING and see a way to use it in your hobby!"
"For instance, Tom Bethel, in his review of the film, says that you are a biologist (as opposed to a hobbyist, which is what I've heard most often you describing yourself as) and that you conceal your identity "for obvious reasons.""
"What is great for a hobbyist is a nightmare in a professional setting."