black jack

plural black jacks

1. countableuncountableAny of certain species of Caranx of gamefish, including C. latus and C. crysos, but especially Caranx lugubris.
2. countableuncountableCertain beggarticks (Bidens spp.), especially Bidens pilosa.
3. countableobsoleteuncountableLarva of a turnip sawfly (Athalia rosae)

   There is a sort of black caterpillar called a black jack, which is seldom seen; but when they do come, they make terrible havock.

   1807, Richard Parkinson, The Experienced Farmer, Enlarged and Improved, page 370

   Synonyms: black canker, black palmer, nigger

4. countableuncountablebusinessSphalerite.
5. countableuncountableA tufted or ring-necked scaup duck (Aythya collaris).
6. alternativecountableuncountableAlternative form of blackjack.
7. countableuncountableUsed other than figuratively or idiomatically: see black, jack.

1. A city in Saint Louis County, Missouri, United States, named for a grove of blackjack oaks.