(n.) A concave surface, or the space bounded by it; the state of being concave.

aduncity alveolation alveolus antrum aquilinity arching arcuation armpit basin boss bowl bump cavity circularity colophon concameration concave convexity convolution crater crookedness crypt cup curvation curvature curving curvity dactylogram dactylograph de-escalation debasement decurvation decurvature degradation demotion dent depression descent detrusion diminution dint dip ducking embossment excrescence excurvation excurvature fingerprint fold follicle footmark footprint footstep fossil footprint funnel chest hauling down hole hollow hollow shell hollowness hookedness ichnite ichnolite impress impression imprint incurvation incurvature incurvity indent indentation indention lacuna lowering lump pad paw print pawmark pimple pit pocket print pug pugmark punch bowl recurvation recurvature recurvity reduction rondure rotundity sag scoop seal shell sigil signet sink sinkage sinkhole sinking sinuosity sinuousness sinus socket stamp step stud submergence thrusting under thumbmark thumbprint tortuosity tortuousness trough vaulting vestige vug