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Related to big on: big brother
big on (something)
Very interested or invested in something. My sister loves going to clubs because she's really big on dancing. My family is big on education, so I know I'm going to college next year.
Enthusiastic about, as in Dad is big on Christmas with the whole family. [Slang; mid-1800s]
Enthusiastic about; partial to: "a patriotic youth organization big on military-style marching drills" (Earl Swift).