adj

• (obsolete) Not deep in tone.
  "the sound perfecter and not so shallow and jarring"
• (tennis) Not far forward, close to the net.
  "Rosol spurned the chance to finish off a shallow second serve by spooning into the net, and a wild forehand took the set to 5-4, with the native of Prerov required to hold his serve for victory."
• (of an angle) Not steep; close to horizontal.
  "a shallow climb"

noun

• (historical) A costermonger's barrow.
  "You might have gone there quite as easily, and enjoyed yourself much more, had your mode of conveyance been the railway, or a hansom, or even a costermonger's shallow."

verb

• (ambitransitive) To make or become less deep.
  "The shallowing of Cenozoic age-frequency curves from tropics to poles thus appears to reflect the decreasing probability for genera to reach and remain established in progressively higher latitudes ( 9 )."