The term 'Horn In (On)' can be summarized by three crossword solutions: IMPOSE (6 letters), ENCROACH (8 letters), and GORE (4 letters). IMPOSE means to force or compel someone to accept something, while ENCROACH means to advance beyond the usual limits. Finally, GORE means to pierce with a horn or tusk. All three words are related to the phrase 'Horn In (On)', which is an idiom meaning to intrude or interfere in someone else's business.