What does "concave" mean?

Concave: Hollow; void of contents. [R.] As concave . . . as a worm-eaten nut. Shak.

Additional senses

  1. 2.A hollow; an arched vault; a cavity; a recess. Up to the fiery concave towering hight. Milton.
  2. 3.(Mech.) A curved sheath or breasting for a revolving cylinder or roll.
  3. 4.To make hollow or concave.

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