any of various testing devices or substances as (1) a pointed metal tip for making electrical contact with a circuit element being checked (2) a usually small object that is inserted into something so as to test conditions at a given point (3) a device used to penetrate or send back information especially from outer space or a celestial body (4) a device (as an ultrasound generator) or a substance (as radioactively labeled DNA) used to obtain specific information for diagnostic or experimental purposes
10-100