Entry 2 senses · 2 variants Webster, 1913 Gonidium · Go·nid·i·um · IPA n. n. 01 n. A special groove or furrow at one or both angles of the mouth of many Anthozoa. 1. A special groove or furrow at one or both angles of the mouth of many Anthozoa.(Zool.) 02 n. A component cell of the yellowish green layer in certain lichens. pl. Gonidia ((#)) 1. A component cell of the yellowish green layer in certain lichens.(Bot.)