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"money," c.1918, American English slang, perhaps from smack (v.1) on notion of something "smacked" into the palm of the hand. Extended form smackeroo is attested from 1939.
Heroin; horse, shit: The cocaine pulled from the front while the smack pushed from the back. It was an incredibly intense high
[1942+ Narcotics; fr Yiddish shmek, ''a smell, sniff''; an earlier sense was ''a small packet of drugs,'' hence merely a sniff or whiff]