Shallow

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late Middle English: obscurely related to shoal2.

wiktionary

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From Middle English schalowe(“not deep, shallow”); apparently related to Middle English schalde, schold, scheld, schealde(“shallow”), from Old English sċeald(“shallow”), from Proto-Germanic *skal-, from Proto-Indo-European *(s)kelh₁-(“to parch, dry out”). [1] Related to Low German Scholl(“shallow water”). See also shoal.

etymonline

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shallow (adj.)

c. 1400, schalowe "not deep," probably from or related to Old English sceald (see shoal (n.)). Of breathing, attested from 1875; of thought or feeling, "superficial," by 1580s. The noun, usually shallows, is first recorded 1570s, from the adjective.