obsidian UK /ˌɒbˈsɪd.i.ən/US /əbˈsɪd.i.ən/noun 2adjective 1forms 3 noun2 •A type of naturally occurring black glass produced by volcanoes. •A slightly bluish black, the color of obsidian glass. adjective1 •(literary) Black. formsobsidians · more obsidian · most obsidian
