Tap1  —n. 1 device by which a flow of liquid or gas from a pipe or vessel can be controlled. 2 tapping of a telephone etc. 3 taproom. —v. (-pp-) 1 provide (a cask) or let out (liquid) with a tap. 2 draw sap from (a tree) by cutting into it. 3 obtain information or supplies from. 4 extract or obtain; discover and exploit (mineral wealth waiting to be tapped; tap skills of young people). 5 connect a listening device to (a telephone etc.).  on tap 1 ready to be drawn off by tap. 2 colloq. Freely available. [old english]