Entry 1 sense Webster, 1913 Costate /(k?s"t?t)/ · Cos·tate · IPA /ˈkɒsteɪt/ 01 a. Having ribs, or the appearance of ribs; (Bot.) having one or more longitudinal ribs. 1. Having ribs, or the appearance of ribs; (Bot.) having one or more longitudinal ribs.(Bot.)