- 11a marine fish that is typically laterally compressed with a row of large spiky scales along each side, important in many places as food or game fish. Also called pompano, scad.[originally a West Indian term]
- Family Carangidae (the jack family): many genera and numerous species. The jack family also includes the horse mackerel, pilotfish, kingfishes, and trevallies
- 14US informalshort for jack shit.
late Middle English: from Jack, pet form of the given name John. The term was used originally to denote an ordinary man (1sense 6), also a youth (mid 16th century), hence the 'knave' in cards and 'male animal'. The word also denoted various devices saving human labour, as though one had a helper (1sense 1, 1sense 3, 1sense 9, 1sense 10, and in compounds such as jackhammer and jackknife); the general sense 'labourer' arose in the early 18th century and survives in cheapjack, lumberjack, steeplejack, etc. Since the mid 16th century a notion of 'smallness' has arisen, hence 1sense 4, 1sense 5, 1sense 7, 1sense 13