- A leather-covered bludgeon with a short, flexible shaft or strap, used as a hand weapon.
- A card game in which the object is to accumulate cards with a higher count than that of the dealer but not exceeding 21.
- To hit or beat with a blackjack.
- To coerce by threats.
- A common <xref>gambling</xref> <xref>card game</xref> in <xref>casinos</xref>, where the object is to get as close to 21 without going over.
- A hand in the game of blackjack consisting of a <xref>face card</xref> and an <xref>ace</xref>.
- The <xref>flag</xref> (i.e., a <xref>jack</xref>) traditionally <xref>flown</xref> by <xref>pirate</xref> <xref>ships</xref>; popularly thought to be a white <xref>skull</xref> and <xref>crossed</xref> <xref>bones</xref> on a black field (the <xref>Jolly Roger</xref>). In older literature sometimes spelled "black jack".
- a small, flat, <xref>blunt</xref>, usually <xref>leather</xref>-covered instrument loaded with heavy material such as <xref>lead</xref> or <xref>ball bearings</xref>.
- a type of weed, Bidens pilosa, in the family <xref>Compositae</xref>.
- To <xref>strike</xref> with a blackjack or similar weapon.
- exert pressure on someone through threats
- a flag usually bearing a white skull and crossbones on a black background; indicates a pirate ship
- a gambling game using cards; the object is to hold cards having a higher count than those dealt to the banker up to but not exceeding 21
- a piece of metal covered by leather with a flexible handle; used for hitting people
- a common scrubby deciduous tree of central and southeastern United States having dark bark and broad three-lobed (club-shaped) leaves; tends to form dense thickets