Intrusive may refer to: Intrusiveness, a typically unwelcome behavior, interrupting and disturbing to others Intrusive rock, intrusion of molten magma leaving behind igneous rock Saltwater intrusion, the movement of saline water into freshwater aquifers Intrusive thought, an unwelcome involuntary thought, image, or unpleasant idea Linking and intrusive R, in phonetics See also Intruder (disambiguation) Invasive (disambiguation)