noun

• The forcible inclusion or entry of an external group or individual; the act of intruding.
• (geology) Magma forced into other rock formations; the rock formed when such magma solidifies.
• A structure that lies within a historic district but is nonhistoric and irrelevant to the district.
• (phonology) The insertion of a phoneme into the pronunciation of a word despite its absence from the spelling. (e.g. intrusive r)