From Longman Dictionary of Contemporary Englishhorn in phrasal verb American English informalINTERRUPTto interrupt or try to take part in something when you are not wanted SYN butt in on Don’t try and horn in on our fun. → horn→ See Verb table
Examples from the Corpus
horn on• For a while, being there felt like horning in on a family reunion.• Several companies have tried to horn in on the market for computer chips like Intel's. 