shallow adj.

c. 1400, schalowe, shaloue, "not deep" (of water, a river, etc.); also of the human body, "thin, emaciated," probably from the same source as Old English sceald "shallow" (see shoal (n.)), perhaps as an abbreviated form of *scealdig. Of breathing, attested from 1875; of thought or feeling, "superficial," by 1580s. Related: Shallowly; shallowness. The noun, usually shallows, "place where water is not deep" is recorded from 1570s, from the adjective.