SYN: Cavity, hole, nook, recess, retreat.
ANT: Coin, abutment, prominence, salience, angle, protrusion, elbow, protection, convexity.
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KEY: Cornice.
SYN: Beading, moulding, projection.
ANT: Entablature, fluting, corrugation, cavity, groove.
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KEY: Corollary.
SYN: Inference, deduction, additament, superaddition.
ANT: Problem, proposition.