shad

noun, plural (especially collectively) shad, (especially referring to two or more kinds or species) shads.

1. a deep-bodied herring, Alosa sapidissima, of Europe and North America, that migrates up streams to spawn, used for food.
2. any other fish of the genus Alosa or related genera.
3. any of several unrelated fishes.

noun plural shad or shads

1. any of various herring-like food fishes of the genus Alosa and related genera, such as A. alosa (allis shad) of Europe, that migrate from the sea to freshwater to spawn: family Clupeidae (herrings)
2. any of various similar but unrelated fishes

n.Old English sceadd “shad,” important food fish in the Atlantic, possibly from Scandinavian (cf. Norwegian dialectal skadd “small whitefish”); but cf. Welsh ysgadan (plural), Irish and Gaelic sgadan “herring.” OED says Low German schade may be from English. Its importance suggested by its use in forming the common names of U.S. East Coast plants and wildlife whose active period coincides with the running of the shad up rivers, e.g. shad-bird, shad-bush, shad-flower, shad-fly, shad-frog. From the shape of the fish comes shad-bellied, 1832 in reference to persons, “having little abdominal protuberance;” of coats (1842) “sloping apart in front, cut away,” especially in reference to the characteristic garb of male Quakers.