ex·tru·sive I. \ikˈstrüsiv, (ˈ)ek|s-, -üziv\adjective Etymology:extrusion + -ive : of, relating to, or produced by geological extrusion < volcanic eruptions and other extrusive phenomena > < extrusive rocks formed after lava reached the earth's surface > — contrasted with intrusive II. noun (-s) : a mass (as an igneous rock) produced by geological extrusion