formation - natural process that causes something to form; "the formation of gas in the intestine"; "the formation of crystals"; "the formation of pseudopods"

covering, natural covering, cover - a natural object that covers or envelops; "under a covering of dust"; "the fox was flushed from its cover"

calculus, tophus, tartar - an incrustation that forms on the teeth and gums

decoration, ornament, ornamentation - something used to beautify