HORN IN is an idiom that means to interject oneself into a situation without being invited. The crossword solutions for this term are INTERFERE (9 letters), TOOT (4 letters), and IMPOSE (6 letters). INTERFERE means to get involved in something that is not one's concern, while TOOT means to blow a horn or make a loud sound. IMPOSE means to force something on someone else. All three words can be used to describe the act of HORN IN, which is to intrude into a situation without being asked.