cactoid,a.Bot.|ˈkæktɔɪd| [f. cact-us + -oid.] Resembling the cactus in form or structure. 1878Hooker & Ball Marocco 328 The curious cactoid Euphorbia, producing the Gum Euphorbium.1885J. Ball in Jrnl.Linn.Soc. XXII. 3 Cactoid plants..are seen on the rocky slopes.