- shoal (n.1)
- "place of shallow water," c.1300, from Old English schealde (adj.), from sceald "shallow," from Proto-Germanic *skala- (cf. Swedish skäll "thin;" Low German schol, Frisian skol "not deep"). The terminal -d was dropped 16c.
- shoal (n.2)
- "large number" (especially of fish), 1570s, apparently identical with Old English scolu "band, troop, school of fish," but perhaps rather a 16c. adoption of cognate Middle Dutch schole, both from Proto-Germanic *skulo- (cf. Old Saxon scola "multitude," West Frisian skoal), perhaps with a literal sense of "division," from PIE root *skel- "to divide." Related to school (n.2) "a crowd of fish." For possible sense development, cf. section from Latin secare "to cut."