freak vs gym rat

freak and gym rat both are nouns.

Word	Noun	Adjective	Verb	Adverb
freak	Yes	No	Yes	No
gym rat	Yes	No	No	No

As nouns, gym rat is a hyponym of freak; that is, gym rat is a word with a more specific, narrower meaning than freak:

freak: someone who is so ardently devoted to something that it resembles an addiction
gym rat: someone who spends all leisure time playing sports or working out in a gymnasium or health spa

freak (noun)	gym rat (noun)
a person or animal that is markedly unusual or deformed	someone who spends all leisure time playing sports or working out in a gymnasium or health spa
someone who is so ardently devoted to something that it resembles an addiction

freak (verb)	gym rat (verb)
lose one's nerve