jig·ger 1 
(jĭgər)
(jĭgər)n.
1. A person who jigs or operates a jig.
2.
a. A small measure for liquor, usually holding 1 1/2 ounces.
b. This amount of liquor.
3. A device, such as a drill, that operates with a jerking or jolting motion.
4. Nautical
a. A light all-purpose tackle.
b. A small sail set in the stern of a yawl or similar boat.
c. A boat having such a sail.
d. A jigger mast.
5. Informal An article or a device, the name of which eludes one.