What does "tap" mean?

Additional senses

1. 2.A gentle or slight blow; a light rap; a pat. Addison.
2. 3.A piece of leather fastened upon the bottom of a boot or shoe in repairing or renewing the sole or heel.
3. 4.pl. (Mil.) A signal, by drum or trumpet, for extinguishing all lights in soldiers' quarters and retiring to bed, -- usually given about a quarter of an hour after tattoo. Wilhelm.
4. 5.To strike a gentle blow.
5. 6.A hole or pipe through which liquor is drawn.
6. 7.A plug or spile for stopping a hole pierced in a cask, or the like; a faucet.
7. 8.Liquor drawn through a tap; hence, a certain kind or quality of liquor; as, a liquor of the same tap. [Colloq.]
8. 9.A place where liquor is drawn for drinking; a taproom; a bar. [Colloq.]
9. 10.(Mech.) A tool for forming an internal screw, as in a nut, consisting of a hardened steel male screw grooved longitudinally so as to have cutting edges. On tap. (a) Ready to be drawn; as, ale on tap. (b) Broached, or furnished with a tap; as, a barrel on tap. -- Plug tap (Mech.), a screw-cutting tap with a slightly tapering end. -- Tap bolt, a bolt with a head on one end and a thread on the other end, to be screwed into some fixed part, instead of passing through the part and receiving a nut. See Illust. under Bolt. -- Tap cinder (Metal.), the slag of a puddling furnace.
10. 11.To pierce so as to let out, or draw off, a fluid; as, to tap a cask, a tree, a tumor, etc.
11. 12.Hence, to draw from (anything) in any analogous way; as, to tap telegraph wires for the purpose of intercepting information; to tap the treasury.
12. 13.To draw, or cause to flow, by piercing. Shak. He has been tapping his liquors. Addison.
13. 14.(Mech.) To form an internal screw in (anything) by means of a tool called a tap; as, to tap a nut.