Source : Webster's Revised Unabridged Dictionary (1913)

Costly \Cost"ly\ (k?st"l?; 115), a. [From Cost expense.]
   1. Of great cost; expensive; dear.

            He had fitted up his palace in the most costly and
            sumptuous style, for the accomodation of the
            princess.                             --Prescott.

   2. Gorgeous; sumptuous. [Poetic.]

            To show how costly summer was at hand. --Shak.

Source : WordNet®

costly
     adj 1: entailing great loss or sacrifice; "a dearly-won victory"
            [syn: {dearly-won}]
     2: having a high price; "costly jewelry"; "high-priced
        merchandise"; "much too dear for my pocketbook"; "a pricey
        restaurant" [syn: {dear(p)}, {high-priced}, {pricey}, {pricy}]
     [also: {costliest}, {costlier}]