Tap, v. t. 1. To pierce so as to let out, or draw off, a fluid; as, to tap a cask, a tree, a tumor, etc.
2. Hence, to draw from (anything) in any analogous way; as, to tap telegraph wires for the purpose of intercepting information; to tap the treasury.
3. To draw, or cause to flow, by piercing. Shak.
He has been tapping his liquors. Addison.
4. (Mech.) To form an internal screw in (anything) by means of a tool called a tap; as, to tap a nut.