Any of various dark-finned fishes; especially (more fully "blackfin tuna") a small tuna of the western Atlantic, Thunnus atlanticus, having the second dorsal fin and the dorsal finlets all dark.
Origin
Early 19th century.
Definition of blackfin in US English:
blackfin
noun
Any of various dark-finned fishes; especially (more fully "blackfin tuna") a small tuna of the western Atlantic, Thunnus atlanticus, having the second dorsal fin and the dorsal finlets all dark.