n. (pl. same or mackerels) a N. Atlantic marine fish, Scomber scombrus, with a greenish-blue body, used for food.
Phrases and idioms:
mackerel shark a porbeagle. mackerel sky a sky dappled with rows of small white fleecy clouds, like the pattern on a mackerel's back.
Etymology: ME f. AF makerel, OF maquerel