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vulgar slang Anything or any amount (of something) at all. Always used in negative constructions to express a complete and utter lack of something. Just shut up, Tom. You don't know jack-shit about marketing. I spent a whole day in the library doing research, but I didn't find jack-shit to use for my thesis.
1. n. a stupid and worthless person. (Usually refers to a male. Usually objectionable.) What a jack-shit! Not a brain in his head!
2. n. anything; anything at all. (Always in a negative expression.) This whole thing isn’t worth jack-shit!