A permanent marker with a fine tip that writes on many surfaces, or a person who is smart and clever.
Trade name created in the 1950s by Sanford Ink Company, likely from the sharp point of the marker. The term became so popular it's now used generically for permanent markers.
Sharpie is a brand name that became a generic term—we call all permanent markers 'Sharpies' now, similar to how people say 'Kleenex' for tissues. This happens when a brand is so dominant it basically owns the category.
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