venta

OED doesn't have an entry for Rapper, in your sense. Although they do have:

1. 1.
   1. One who raps or knocks; a spirit-rapper.
   
   
   2. slang. One who tells a downright lie; a professional perjurer. Cf. sense 3a and RAPPING vbl. n.1 2b. Obs.
   
   
   3. U.S. slang. A complainant, plaintiff; a prosecutor. Cf. RAP v.1 1c.
   
   
   4. An itinerant purchaser of antiques; esp. one who buys valuable objects cheaply from credulous householders. Cf. KNOCKER 2e.
   
   
   5. U.S. slang. A talker; a chatterer. Cf. RAP v.1 3d.


2. Anything used for rapping; spec.
   1. A door-knocker. Obs.
   2. A rattle or clapper. rare.
   3. Coal-mining (see quot. 1851).


3. 1. An arrant lie; a downright falsehood. Now only dial.
   
   
   2. A great oath. Now only dial.


4. Something remarkably good or large. Obs. (Cf. RAPPING ppl. a. 2.)

The 1851 quote is

1851 GREENWELL Coal-trade Terms, Northumb. & Durh. 41 Rapper.A lever, placed at the top of a shaft or inclined plane,..to give signals, when every thing is ready at the bottom for drawing away

, which does match (roughly) what you suggested yesterday.


We do have, under rapping, vbl. n.1

3.attrib., as rapping bar, a pointed iron bar used in founding for loosening patterns from moulds; rapping iron, an implement used in basketry to tap the rows of weaving into the desired position; rapping plate Founding, a metal plate attached to a pattern in order to prevent damage to the pattern when it is loosened from the mould.

, which may or may not be relevant.

We've only got one quote about rapper as a dance (rather than rap music), and it's probably fairly near update time. So find the written documentation quickly! (How to contribute words to the Reading Programme).