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"important person," 1929, American English, from Prohibition-era gangster slang; earlier in the same sense was great shot (1861). Ultimately a reference to large type of gunshot.
•Often used sarcastically: a big-shot chest surgeon/ big-shot notionsn phr,n
A very important person; influential person; leader; big cheese, biggie •Thought to have been taken over from the idiom of Prohibition-age gangsters: eight big shots of various farmers', manufacturers', or veterans' organizations/ ''Hey, bigshot,'' his father would bellow on the telephone (1920s+)