shoal vs sandbank

shoal and sandbank both are nouns.

Word	Noun	Adjective	Verb	Adverb
shoal	Yes	No	Yes	No
sandbank	Yes	No	No	No

As nouns, sandbank is a hypernym of shoal; that is, sandbank is a word with a broader meaning than shoal:

shoal: a sandbank in a stretch of water that is visible at low tide
sandbank: a submerged bank of sand near a shore or in a river; can be exposed at low tide

shoal (noun)	sandbank (noun)
a large group of fish	a submerged bank of sand near a shore or in a river; can be exposed at low tide
a stretch of shallow water
a sandbank in a stretch of water that is visible at low tide

shoal (verb)	sandbank (verb)
become shallow
make shallow