| 1. | a short, leather-covered club, consisting of a heavy head on a flexible handle, used as a weapon. |
| 2. | Cards.
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| 3. | black flag (defs. 1, 2). |
| 4. | a small oak, Quercus marilandica, of the eastern U.S., having a nearly black bark and a wood of little value except for fuel. |
| 5. | a large drinking cup or jug for beer, ale, etc., originally made of leather coated externally with tar. Compare bombard (def. 7). |
| 6. | caramel or burnt sugar for coloring spirits, vinegar, coffee, etc. |
| 7. | Mineralogy. a dark, iron-rich variety of sphalerite. |
| 8. | to strike or beat with a blackjack. |
| 9. | to compel by threat. |
| 1. | a pirate flag, usually of black cloth with a white skull and crossbones on it; Jolly Roger. |
| 2. | a flag having two yellow and two black squares, signifying the letter L in the International Code of Signals: formerly so called when used by itself to indicate the presence of cholera on board a vessel. |
| 3. | a signal given to an automobile racing driver to stop, usually because the car may have a dangerous problem that requires inspection. |
| 1. | John Joseph (“Blackjack” ), 1860–1948, U.S. general: commander of the American Expeditionary Forces in World War I. |
| 2. | Military.
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| 1. | a cardinal number, 20 plus 1. |
| 2. | a symbol for this number, as 21 or XXI. |
| 3. | a set of this many persons or things. |
| 4. | Also, 21. Also called blackjack. a gambling game at cards, in which the object is to obtain from the dealer cards whose values add up to, or close to, 21 but which do not exceed it. |
| 5. | amounting to 21 in number. |