Intrude, with "in" (4)
I believe the answer is:
horn
'intrude with in' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for horn that I've seen before include "familiar to the matador?" , "Musical instrument; Chile Cape" , "Instrument - rhino's appendage" , "Musical instrument - antler" , "Brass musical instrument" .)