What is the meaning of shoal?

noun

• A sandbank in a stretch of water that is visible at low tide.
• A stretch of shallow water.
  • synonyms: shallow
• A large group of fish.
  • usage: "a school of small glittering fish swam by"
  • synonyms: school

verb

• Make shallow.
  • usage: "The silt shallowed the canal"
  • synonyms: shallow
• Become shallow.
  • usage: "the lake shallowed over time"
  • synonyms: shallow