Merriam-Webster Collegiate Dictionary - shoal

 I. adjective  Etymology: alteration of Middle English shold, from Old English sceald — more at skeleton  Date: circa 1554 shallow  II. noun  Date: 1555  1. shallow  2. a sandbank or sandbar that makes the water shallow  III. verb  Date: 1574  intransitive verb to become shallow  transitive verb  1. to come to a shallow or less deep part of  2. to cause to become shallow or less deep  IV. noun  Etymology: Middle English *shole, from Old English scolu multitude — more at school  Date: 1579 a large group or number ; crowd a ~ of fish  V. intransitive verb  Date: 1610 throng, school