concavity
US /ˌkɑːnˈkæv.ə.t̬i/
UK /ˌkɑːnˈkæv.ə.t̬i/
1.
the quality of curving in, or an object or surface that curves in:
:
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The valley looks utterly serene now - a spacious concavity lying between pine-clad peaks.
the quality of curving in, or an object or surface that curves in: