in·ter·nal (ĭn-tûr′nəl) adj. 1. Of, relating to, or located within the limits or surface; inner. 2. Residing in or dependent on essential nature; intrinsic: the internal contradictions of the theory. 3. Located, acting, or effective within the body. 4. Of or relating to mental or spiritual nature: "An internal sense of righteousness dwindles into ....