Entry 1 sense Webster, 1913 Ostreaceous · Os·tre·a·ceous · IPA /ˌɒstɹiˈeɪʃəs/ 01 a. Of or pertaining to an oyster, or to a shell; shelly. 1. Of or pertaining to an oyster, or to a shell; shelly.(Zool.) “The crustaceous or ostreaceous body.” — Cudworth.