noun

• One who, or that which, raps or knocks.
• The knocker of a door.
• (historical, mining) A swinging knocker for making signals at the mouth of a shaft.
• A spiritualistic medium who claims to receive communications from spirits in the form of knocking sounds.
• (music) A performer of rap music, or someone who raps in any form of music.
• (obsolete, Scotland) A sword.
• A flexible strip of metal, 45-60cm long, with handles at each end, used for Northumbrian rapper sword dancing.
• A mechanical, or later electric, signalling device formerly used in the mines of north-eastern England to signal to the engineman that the cages carrying men or coals up and down the shaft were ready to be raised or lowered.
• (colloquial, dated) A bold lie; a whopper.
• (colloquial, dated) A loud oath.