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Webster 1913 Edition

Noun.

The quality or state of being plain.

Noun.

Levelness; evenness or surface.

Want of ornament; want of artificial show.

So modest plainness sets off sprightly wit.

Openness; rough, blunt or unrefined frankness.

Your plainness and your shortness please me well.

Artlessness; simplicity; candor; as unthinking plainness.

Clearness; openness; sincerity.

Seeing then we have such hope, we use great plainness of speech. 2 Cor.3.

plainness ‎(usually uncountable, plural plainnesses)