Godan verb with 'ru' ending, Intransitive verb
to shut oneself in (one's house, room, etc.); to confine oneself (to)
しかし王女は部屋に立てこもって出てこなかった。However, the princess had barricaded herself in her room and wouldn't come out. to barricade oneself (in a building); to entrench oneself; to hole up; to hold (a castle, etc.)
Also written 立て篭もる【たてこもる】、立て籠もる【たてこもる】、楯籠る【たてこもる】