"large number" (especially of fish), 1579, apparently identical with O.E. scolu "band, troop, school of fish," but perhaps rather a 16c. adoption of cognate M.Du. schole, both from P.Gmc. *skulo- (cf. O.S. scola "multitude," W.Fris. skoal), perhaps with a lit. sense of "division," from PIE base *skel- "to divide." Related to school "a crowd of fish" (q.v.). For possible sense development, cf. section from L. secare "to cut."
On the 16th of November, in the afternoon, we lost a boat during our work in a shoal of whales. I was in the boat myself, with five others, and was standing in the fore part with the harpoon in my hand, well braced, expecting every instant to catch sight of one of the shoal which we were in so that I might strike.