Entry 2 senses Webster, 1913 Costly /(k?st"l?; 115)/ · Cost·ly · IPA /ˈkɒst.li/ 01 a. Of great cost; expensive; dear. 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.